This mod can probably best be summarised as bringing about the following changes:

• Make NG+ more challenging compared to vanilla.
• Bring Geralt closer to the lore established by the books (gameplay wise)
• Various gameplay improvements/skill re-designs that, in my personal opinion, improve the combat system
  

Although these metrics ended up being the core bulk of the mod in the end, I didn't set out with them in mind. In fact, I ended up modding the game as I played - making small changes here and there that I thought would improve the experience. In the end, I got something as described above. This makes it somewhat difficult to summarise exactly what this mod does in a concise way. So instead, I'll provide a brief summary followed by all the changes the mod makes in meticulous detail. But, before we begin that:

FULL DISCLAIMER: This is the first mod I have made for anything... ever. I don't even know if it will work (it does in my version of the game at least!) In saying that, I will strive to resolve any issues people may bring up to the best of my ability. 

With that out of the way, let's jump in:

SUMMARY
I guess the first thing to note would be that this mod has been designed with NG+ in mind. In fact, the mod probably won't function with normal New Game and would be completely unbalanced anyway. 

As for the specific changes, most large monsters in the game have been given a large health, attack power and resistance boost. I wanted to try and lower the discrepancy between fighting large one-on-one monsters (i.e. griffins) and group monsters (i.e drowners). I found that in most cases, fighting the latter was usually far more daunting than fighting the former, where as it should really be the other way around. To combat this, large monsters now pack a bigger punch so you really need to make sure you have your wits about you when facing them. This applies even more so for contract monsters. 

Next up were key changes to both the combat and alchemy systems. In terms of combat, a number of skills were changed, ranging both from minor changes to complete overhauls. In summary, adrenaline is now a much more important component of combat though a lot harder to generate. Some alchemy skills have been modified as well, though the main change to alchemy has been how toxicity works. Max Toxicity for even a dedicated alchemy build has dropped by almost 50%, and potion toxicity has also been increased. It is not possible to run around with three decoctions active with this mod (well... at least not until very late end game). This change was made for lore reasons as much as gameplay. Geralt shouldn't be chugging potions - instead potions should be used when necessary. To balance these changes, potion effects have been improved - drastically in some cases. Furthemore, oils have been buffed drastically to make preparation more important and most decoctions have been overhauled to be less situational

You may be wondering why I haven't mentioned any sign changes. That's mostly because there weren't any, except for one minor change to Quen. This is due to two reasons:

• As part of the lore, signs were never a witcher focus - more of a supplement. In fact, I would say that the way signs are portrayed in the game are already far too over-powered. 
• I've never played a dedicated sign build, and so therefore I don't believe I have the knowledge on how it can be improved.
  

Suffice to say, a dedicated sign-build probably won't mesh well with this mod. 

WILD HUNT CHANGES
GENERAL

• Sprinting/Jumping outside of combat costs no Stamina
• Geralt can parry arrows from the start - no skill required. He doesn't have amnesia anymore, so him forgetting how to parry arrows between games doesn't make sense
• Strong attacks do 33% more damage
• Improved Stats on Winter's blade (sword given by Crache). They are no longer auto-generated and the sword will always be given at Geralt's level
• Toxic Face thresholds increased from <25%/<50%/<75%/75%+ to <45%/<65%/<85%/85%+
• Arbitrary huge stat bonuses based on level difference removed. A guard can't beat Geralt - that's ridiculous. 
• Followers such as Vesemir, Triss and Yen will do 250% more damage.
• Weapons degrade 25% slower
• Bosses (i.e Wild Hunt) always scale to Geralt's level. These guys should always be a challenge
  

ADRENALINE

• Adrenaline drains 50% faster outside of combat
• Sword attacks generate adrenaline 50% slower
• Signs generate adrenaline 30% slower
• Crossbows generate adrenaline 20% slower
• Bombs generate adrenaline 20% slower
• Finishers generate 0.1 Adrenaline Points
• Getting hit with a light/heavy/super heavy (i.e. fiend) attack drains 50%/80%/150% more adrenaline, respectively
• Geralt will still lose adrenaline when hit with an active Quen
  

COMBAT SKILLS

• Whirl: Lowered Adrenaline cost by 50%
• Arrow Deflection: Since Geralt can now parry arrows with no skill, this has been overhauled. Also, since Geralt isn't a Jedi, I removed the original effect of level 3. Instead, deflecting an arrow will now generate 0.1 Adrenaline Points per skill level 
• Counterattack: Also overhauled. When a successful counter is performed, each Adrenaline Point increases the chances of performing an immediate finisher. If a finisher is activated, 1 Adrenaline Point is consumed. At max level and three Adrenaline Points, there is a 60% chance of a finisher activating
• Razor Focus: Minor change to move the "instantly gain 1 Adrenaline Point" when entering combat to level 5.
• Flood of Anger: Also overhauled and probably my favourite change. It never made sense to me that the ultimate adrenaline ability in the combat tree was sign related. Instead, once 3 Adrenaline Points are reached, they will immediately be consumed to enter a "battle trance" mode in which time is slowed down. The extent of the time dilation and the duration is dependant on both the level of the skill and the number of enemies being faced (a modified old version of Flood of Anger still exists as part of a change to the Foglet Decoction for those who liked it)
  

SIGN SKILLS

• Quen (basic version): The stamina delay after casting Quen has been increased from 0.5 seconds to 2 seconds. Also, one second gets added to the delay each time Quen breaks in a single combat scenario, up to a maximum of 10 seconds. This discourages tactics of just casting Quen each time it breaks - it should only be used against monsters that cause large damage when they hit you.
  

ALCHEMY SKILLS

• Acquired Tolerance: Lowered toxicity point gain per formulae from 1 to 0.5 points
• Fixative: Overhauled. Each level now lowers the targeted monster's physical resistance by 5%. This basically means you'll do 15% more total damage at level 3 with the correct oil applied. (A modified version of the old Fixative skill still exists on the Grandmaster Wolf Gear)
• Side Effects: Removed Killer Whale potion from the potential random potions pool
  

POTIONS

• Thunderbolt: Attack Power bonus increased from 35% to 45%. Toxicity increased from 25 to 30. Removed superior storm effect, adds reliable 5% critical chance instead.
• Black Blood: Returned damage increased from 15%/20%/30% to 50%/70%/100%. Toxicity increased from 15/15/15 to 30/30/40
• Full Moon: Vitality bonus increased from 600/1100/1500 to 2000/3000/4000. Toxicity increased from 25 to 40
• Petri's Philtre: Sign Intensity bonus increased from 15%/20%/25% to 20%/30%/50%. Toxicity increased from 25 to 30
• Maribor Forest: Toxicity increased from 20 to 40
• Cat: Charges changed from 3/4/5 to 4/6/8
  

OILS

• Monster oil (all oils except for Beast and Hanged Man's Venom) attack power bonus increased from 10%/25%/50% to 25%/50%/100%
• Enhanced/Superior monster oils now lower the enemy's physical resistance by 10%/20%, respectively
• Can no longer apply oils during combat
  

DECOCTIONS

• Earth Elemental Decoction: Overhauled. Heavy attacks can't be parried by most normal sized enemies
• Basilisk Decoction: Overhauled. Bombs do +100% damage. Duration/toxicity same as other decoctions
• Werewolf Decoction: Overhauled. The lower Geralt's vitality, the higher the damage done
• Wyvern Decoction: Overhauled. Damage done to Geralt increases toxicity before depleting Vitality
• Foglet Decoction: Overhauled. Altered version of old "Flood of Anger" ability. Cast a full powered sign at the cost of 2 Adrenaline Points (no sign intensity bonus). Still has the buggy-ness of the old Flood of Anger, nothing I can do there. 
• Katakan Decoction: Increased critical hit chance from 5% to 10%
• Water Hag Decoction: Increased Attack Power bonus from 50% to 75%
• Troll Decoction: Lowered Vitality regeneration in combat from 100/sec to 50/sec
• Alghoul Decoction: Increased Adrenaline gain from 50% to 70%
• Fiend Decoction: Increased encumbrance bonus from 20 to 50
• Ancient Leshen Decoction: Increased Stamina regeneration bonus from 5/sec to 10/sec
• Leshen Decoction: Increased damage reflect from 2% to 10%
• Griffin Decoction: Increased resistance stack from 1% to 5%, decreased cap from 25% to 20%
• Archgriffin Decoction: Health Reduction increased from 5% to 10%. Uses stamina as well 1 Adrenaline Point. Must have full Stamina for it to work.
• Succubus Decoction: Increased Attack Power bonus stack from 1% to 3%, cap 60%
  

BOMBS

• Dancing Star: Fire damage increased from 100/200/300 to 400/700/1100
• Devil's Puffball: Poison Damage increased from 100/200/300 to 400/700/1100
• Dragon's Dream: Fire Damage increased from 300/450/600 to 900/1500/2000
• Grapeshot: Physical/Silver Damage increased from 350/700/900 to 900/1500/2000
  

MONSTERS/ENEMIES (key: + minor increase, ++ moderate increase, +++ major increase, - minor decrease, -- moderate decrease, --- major decrease)

• Most group monsters (i.e ghouls, nekkers, drowners): health+
• Wolves: health--, attack power--. Wolves should be a minor annoyance, not the most dreaded enemy. 
• Sylvans: health++, physical resistance+
• Gargoyles: health++, physical resistance++
• Arachas: health++, physical resistance++, attack power+
• Berserkers: health++, attack power+
• Werewolves: health+, physical resistance+, attack power++, increased dodge chance
• Katakans/Ekimmaras: health++, physical resistance++, attack power++, increased dodge chance
• Higher Vampires: health+++, physical resistance+++, attack power+++, increased dodge chance
• Trolls: health++, physical resistance++
• Golems: health++, physical resistance++
• Earth Elementals: health++, physical resistance++
• Ice Elementals: health++, physical resistance++, attack power+
• Fire Elementals: health++, physical resistance+, attack power+
• Fiends: health+++, physical resistance++, attack power+
• Chort: health+++, physical resistance++, attack power+
• Ice Giant: health++, physical resistance++, attack power+
• Cyclops: health+++, physical resistance++, attack power+
• Noon/Night/Pesta Wraith: health+, physical resistance+
• Griffin: health++, physical resistance+
• Archgriffin: health+++, physical resistance+, attack power +
• Draconids: health+++, physical resistance+, attack power+++
• Leshen: health+++, physical resistance+, attack power+
• Ancient Leshen/Hym: health+++, physical resistance++, attack power+
• Djinn: health+++
  

• Imlerith (always scales): health+++, physical resistance++, attack power++
• Caranthir (always scales): health++, physical resistance+, attack power+
• Eredin (always scales): health+++, physical resistance+++, attack power-
  

BUG FIXES

• Hunter's Instinct skill was not correctly applying its own level bonuses to its critical hit damage. This has been fixed.
• Quen would sometimes cancel the effect of toxicity on the face when broken. This has been fixed.
  

HEARTS OF STONE CHANGES
The only main issue I had with the first expansion was that most enemies became damage sponges. This seemed like a lazy way of increasing the difficulty, so the mod mainly attempts to combat some of these issues without making it too easy:

MONSTERS/ENEMIES (key: + minor increase, ++ moderate increase, +++ major increase, - minor decrease, -- moderate decrease, --- major decrease)

• Group monsters: health---, attack power---
• Flaming Rose: health---, attack power++, increased parry and dodge chance
• Arachnamorphs: attack power+
• Boars: health---, attack power++
• Bears: health--, attack power+
• Golems: health-, attack power+
• Horst Brothers: health--, attack power++, increased parry and dodge chance
• Wyvern: health-, attack power+
• Caretaker: health++, physical resistance++, attack power++
• Iris: physical resistance++, attack power++
• Olgierd Ghosts: attack power+
• Nightmare Olgierd: health+, attack power+
• Oxenfurt Witchhunters: health--
  

BLOOD AND WINE CHANGES
This was probably the hardest changes to make. On one hand, I wanted this to feel like Geralt's holiday. Its like the epilogue of the series so, difficulty wise, I didn't feel it needed to be insane. By the same token, its also Geralt's final adventure. It needs to be epic. So, I struck a middle ground. Most of the exploration and quests are not too challenging - this is mainly achieved by the vanilla version of the game. As soon as you get Aerondight and Grandmaster Armor, you're basically invincible. To balance this, I've made the vampires drastically stronger. As a rule of thumb, don't even approach them without Grandmaster Armor and Aerondight or something equivalent. 

MUTATIONS

• Conductors of Magic: Increased damage bonus from 50% to 70%
• Bloodbath: Increased Attack Power bonus from 5% to 10%, dropped max cap from 250% to 200%
• Piercing Cold: Changed freeze chance from base 25% to 10% per Adrenaline Point (max 30%), removed extra damage
• Adrenaline Rush: Increased duration from 30s to 45s. Decreased Attack Power bonus from 30% to 25%. Increased debuff max from 70% to 80%
• Deadly Counter: Increased finisher trigger from 25% to 50% Vitality
• Euphoria: Increased bonus from 0.75% to 1% per toxicity point
• Second Life: Decreased cooldown from 180 seconds to 90 seconds
• Metamorphosis: Overhauled. First Decoction drank has no toxicity and either a significantly increased effect or duration (see below for further details). Kept witcher senses enhancement.
  

METAMORPHOSIS

• Alghoul Decoction: Adrenaline Point gain remains even after attacked
• Ancient Leshen Decoction: Duration tripled
• Arachas Decoction: Resist bonus doubled
• Archgriffin Decoction: No longer costs 1 Adrenaline Point
• Basilisk Decoction: Damage bonus doubled
• Chort Decoction: Duration tripled
• Cockatrice Decoction: Adds another alchemy charge (total +2)
• Doppler Decoction: Critical Hit Damage bonus doubled
• Earth Elemental Decoction: Duration tripled
• Ekhidna Decoction: Vitality restore doubled
• Ekimmara Decoction: Vitaliity restore doubled
• Fiend Decoction: Duration tripled
• Foglet Decoction: Only costs 1 Adrenaline Point to cast
• Forktail Decoction: Bonus lasts for entire combat scenario when activated once
• Grave Hag Decoction: Duration tripled
• Griffin Decoction: Resist Cap doubled to 40%
• Katakan Decoction: Critical Hit Chance doubled
• Leshen Decoction: Damage reflect doubled
• Nekker Warrior Decoction: Damage doubled
• Nightwraith Decoction: Duration tripled
• Noonwraith Decoction: Duration tripled
• Reliever's Decoction: Bonuses doubled
• Succubus Decoction: Cap doubled to 120%
• Troll Decoction: Duration tripled
• Water Hag Decoction: Damage doubled
• Werewolf Decoction: Damage doubled
• Wraith Decoction: Quen shield activates at 1/6 Vitality loss
• Wyvern Decoction: Toxicity increase halved
  

GRANDMASTER GEAR

• Manticore Gear changed to a light armor
• Grandmaster Wolf Gear now requires the Mastercrafted Wolf Gear to craft
• Grandmaster Wolf Gear 3/6 bonus overhauled. Changed to level 3 version of old Fixative skill - blade oils don't wear off
  

MONSTERS/ENEMIES (key: + minor increase, ++ moderate increase, +++ major increase, - minor decrease, -- moderate decrease, --- major decrease)

• Group Monsters: health+
• Knight Giant: health++, attack power++
• Shaelmaar: health+++, attack power++
• Slyzards: health+++, physical resistance++, attack power+++
• Banshee: health+++, physical resistance++, attack power+++
• Kikimore: physical resistance+
• Giant Centipede: health++, physical resistance++, attack power++
• Spriggan: health+++, physical resistance++, attack power+++
• Wight: health++, attack power+++
• Arena Knights (Warble quest): health-, attack power-
• Fairy Tale Witch: health+++, physical resistance+, attack power+++
• Fairy Tale Wolf: health+++, physical resistance+++, attack power+++, increased dodge chance
• Cloud Giant: physical resistance+, attack power+++
• All Vampires: health+++, physical resistance+++, attack power+++
• Dettlaff: health+++++++++, physical resistance+++, attack power+++++++++
  

• Greatly increased all stats for monsters during the "Monster Arena" quest
• Greatly increased all stats for vampires during the "Night of Long Fangs" quest
  

BUG FIXES

• Resolved bug where centipede and kikimore discharge and centipede mandible didn't dismantle into Acid Extract
  

WAY TO PLAY
One of the points of this mod is to feel like it is a continuation of the Witcher 2. This is why the changes are meant for NG+, as if you import a save where the main game but not the expansions is complete, you should start at around level 35. Hence, here is my personal guide on the best way to play this mod:

• New Game Plus, obviously.
• Death March Difficulty
• Level 32 - 36 Geralt
• Drop all weapons, armor, decoctions, most potions (can keep some of the basic ones like swallow and tawny owl), alchemy ingredients, crafting supplies
• Keep all recipes
• Add Caerme, Forgotten Vran Sword and Addan Deith through the console (Witcher 2 end game weapons)
• Use the "Shields" mod. Not for the shield combat, but rather the added armors. The Warden Armor looks suspiciously a lot like the Vran Armor from the Witcher 2 end game. This is a good starting armor and makes the game feel like a continuation from Witcher 2. 
  

I've added an optional save file of a level 35 Geralt for anyone that wants to use it with the settings mentioned above. Note that is requires the above mentioned Shields mod. 
If you've made it this far and are willing to try out the mod, I hope you enjoy it! (and that it works :/)