Introduction

BG 3 Shield mechanics is quite simple. Shields add +2 to AC. In some rare circumstances +3. The real distinction is between the shields that allow Bashing and the shield that don't. It's not a bad design. But it also lacks variety and generally less interesting than it could have been. And after separating evasion and damage resistance for armor, some cracks begin to show as now shields become more useful for light armored characters than heavy armored ones. Fully alternative way is to make shields totally about damage resistance, and while a valid approach, it feels a bit weird as real life application of shields more resemble evasion of damage than withstanding it.

Description

This mod overhauls Shields mechanics. It is spiritual successor of Armor Overhaul, but can be used without it just as well. Taking inspiration from already existent parrying related features, it separates light deflection of attacks, represented by passive increase in AC, and full blocking of attacks represented by damage reduction on a reaction. Thus, whether you strategy is based around having high AC or damage reduction, shields can be beneficial for you. And as reactions are a limited resource, even considerably high values of damage reduction from shields are not going to be overpowered.

Shields can block both weapon and magical attacks, whether they are ranged or melee. But there are several limitations.

• Attacks which main component is Poison, Necrotic, Psychic or Force Damage can't be blocked.
• The attack has to be directly targeted at a character. Area effects, such as fireball or ice cone can't be blocked - Shield Master Feat
  allows you to deal with them in it's own way.

Various Shields now have different stats fitting for different play styles. All shields are separated into 5 categories, some are better at deflection and some at blocking:

• Flimsy Shields. Better than nothing but just barely. In addition to their already low AC, allow to block 1 point of damage as a reaction.
  Consist of Toy Shield and Broken Shield.
• Light Shields. Good for deflecting attacks but can't withstand significant direct damage. Add their full bonus to AC and allow to block
  1d4 points of damage. Consist of wooden shields and leather shields.
• Medium shields. A bit worse at deflection a bit better at blocking. Have -1 penalty to AC and allow to block 1d8 points of damage. Consist of Studded Shields, Great Leather Shields, Woadwood and Kua-Toa shields. Rusty shield has the worst of both worlds: -1 AC and 1d4 block.
• Heavy Shields. Can withstand significant direct hits but do not provide any help with deflection. Require considerable Constitution to be used
  effectively. Have -2 penalty to AC and allow to block 2d6 - 1 + ConstitutionModifier/2 points of damage as a reaction. Consist of Great Wooden Shields and Metal Shields.
• Massive Shields. If your Constitution allows to use them, they can withstand even the mightiest of attacks but hamper your evasiveness. Have -3 penalty to AC and allow to block 4d4 - 3 + ConstitutionModifier points of damage as a reaction. Consist of Great Metal Shields.
  

Other features:

• Shields +1 add this bonus both to AC and damage block roll.
• Shield Master Feat additionally allows to add Proficiency Bonus to damage block roll.
• Shields with effects that triggered on a missed attack, now trigger this effect on a block.
  
  

Compatibility and Recommendations

Armor Overhaul - naturally compatible and highly recommended to be used together
Weapon Overhaul - likewise, both three mods follow the same design philosophy
Get Ready - an excellent opportunity to use your shield more often, getting an extra reaction, without upsetting game balance

Shield Mechanics Overhaul - not compatible as it's an alternative approach to the same mechanics. Choose whatever fits you better.