Read changelog and such, but in short:
Some raid bosses now take more melee damage
Some weapon and skill adjustments and such.
Default Game Difficulty: Hardcore.

Use BLCMM to configure animation speed for enemies and other settings to your liking.

Just check changelog.
Some balance fixes and minor bug fixes.
Also reduced the size of shield break particles.

Default Difficulty: Hard.

Default difficulty: Nightmare.

Fixed True Nightmare decreasing damage received by player instead of increasing it. (was ~x0.6 instead of x1.25)
Reworked Flayer and other tiny balance tweaks.

Slight Salvador rework, slight Axton buffs
Piston can now drop up to 5 random legendary shields (pearl if lucky)
Mimics now drop Tiny Tina class mods, up to 4 if lucky
And other misc changes

Just check changelog inside archive. (Previous Version: 21.26F2)
Default Difficulty: Hard (The mod is balanced around Nightmare difficulty)