I can only put so much onto the description page, so if you want more
specifics I'll try to list most of them. To start with, Rare is Better:

Weapons made of the rare materials Glass, Stalhrim, Ebony, Dragonbone, and Daedric have had their base damage buffed by 3-5 points. 2H weapons were favored a little. Tempering works by adding integers (rounded after calculating) to base damage - this means the tempering nerf is no exact formula since the game does not always round to the nearest integer. The end result is that your best potential tempering is now about 4 points weaker, but your best weapons are 3-5 points stronger. A lot of unique weapons were similarly buffed as well (you might actually use The Pale Blade for a while!).

Dragonbone vs Daedric: they have the same damage but Dragonbone's a lot heavier. I felt like this was a reasonable compromise to reward master-level smiths who still haven't unlocked Daedric recipes. Daedric weapons are the same weight as Ebony.

Armors follow similar changes, lightly favoring heavy over light. Since cuirasses get twice the tempering bonus, they received twice the buff. Heavy armors made of rare materials got +4/+8 and light armors got +3/+7. Like with weapons, many unique armors were similarly buffed.
For crafting, there is a 10-point skill requisite penalty to craft racially specific gear (Morrowloot 4E Edition was 20, I felt like that was too restrictive). For example: you need 30 crafting skill to unlock the Elven Smithing perk, but both 40 skill and the perk to craft Elven equipment if you're not a High Elf.

List of armors and their racial affinities or other details:
Elven: High Elves
Thalmor (if using aMidianBorn Content patch): High Elves
Orcish: Orcs
Nordic Carved: Nords (including aMidianBorn variants) (Nord Hero, too, if using Warmonger, which has been adjusted to match Nordic)
Glass: Altmer and Dunmer, if using aMidianBorn then Thalmor is Altmer only and Steel is Dunmer only

also:
Dwarven: only craftable if you have the Ancient Knowledge perk from Unfathomable Depths (except the Crossbow). Ancient Knowledge now also buffs Dwarven Weapons (except the Crossbow), making Dwarven some of the best gear you can craft before you begin obtaining the really rare stuff.
Ebony: only craftable at the Skyforge. Ebony ore and ingots are also much more rare.
Daedric: crafting Daedric is lost knowledge so you're going to have to find knowledge that no other smith in the game will possess. Not gonna spoil where. What I will tell you is that you're working with Ebony, so Skyforge only, and it can only be crafted at night.

Nearly all sources of Fortify Alchemy/Enchanting/Smithing have been removed from the game. Not only do they imbalance the game by design, they invalidate what MLU tries to achieve. There's no point in seeking the best gear in the game if you can just drink a potion and put on your smithing outfit to tempera set of steel plate and hit the armor cap. Leaving some unique sources
of crafting bonuses, such the Ring of Pure Mixtures, Forgemaster's Fingers, or the Ahzidal set bonus (and not disenchantable) rebuilds this broken feature into something that adds real value to the game.

Many alchemical ingredient effects were buffed in addition to the Restore changes (such as longer durations and more useful Ravage poisons) so that your created potions will better compete with found potions. Rare ingredients are stronger now (Nirnroot's actually good!) and Dragon ingredients are especially useful. Enchanting and Smithing were in no need of compensation, although they certainly fill more important roles.

You can still find Dwarvem, Elven, and Orcish equipment in certain random lists. In previous Morrowloots, they were totally removed from anything but deliberate locations - I felt like these items would still have been in circulation, just treated like they're special. I placed them back into "boss", "best", and "special" leveled lists, using WAF as a reference (another reason you should be using the full version of WAF). An example of this in action is that in a group of bandits, most of them will have only common equipment, but the boss might come at you with an Orcish Battleaxe. A lot of quest rewards can also be Elven/Dwarven/Orcish again (still not Glass+).

These crafting changes aren't arbitrary additions: they're necessary to keep MLU from "requiring" other mods to be cohesive. Without them, glaring balance issues would remain and ask you to find other mods to fix them - which is exactly why I made my own version of Morrowloot to
begin with.

Lore Weapon Expansion: I love this mod but they're overpowered for their respective equipment tiers. The patch rebalances them to better fit the point at which you will find or craft them (as well as to match Rare is Better).

Warmonger Armory: This mod compliments vanilla Skyrim perfectly, but for MLU it needs some rebalancing. Nord Hero was nerfed to essentially act as an fancy, alternate version of Nordic Carved - this let me keep them in the leveled lists. Its crafting recipes were altered to match their new stats, placing them in the Nordic category and removing Ebony from their materials. Coupled with the Ancient Nord Hero items added in MLU, these fit into the game perfectly and prices and stats have been carefully coordinated between all three kinds. The rest of the armors in Warmonger were treated similarly (and the same is true for aMidianBorn Content).

A note about Immersive Armors & Immersive Weapons
As-is, they're compatible-ish with inconsistencies. These mods add equipment to all vanilla tiers, and MLU widens those tiers by buffing Glass+ equipment. So IA and IW won't totally break MLU balance since none of it will compete with vanilla's rare items. It will screw with balance up until that point, however, by adding back items of certain power levels where MLU has taken them out. Its crafting recipes will also let you bypass some of MLU's crafting restrictions by letting you craft items equivalent to, say, Orcish before a non-Orc could craft actual Orcish gear. Many of the weapons and
armors are also overpriced and/or overpowered.
A proper MLU patch for IA and IW is on the way. For now, the existing patches will still allow you to add a lot of good stuff to your game.