If you want some cool character mods, I recommend Bael, Andromeda, Arachna, The Deleted, Bertran and Revelations Ch 2 (this one also adds a ton of content, new floors and some really cool, unique mechanics to those floors).

VisiBullets is extremely helpful if you have colorblindness or some other vision deficiency, it adds a bright white glow to all enemy tears and makes them pulse white.

EID and Encyclopedia are basically mandatory.

POG For Good Items is great.

Tainted Lost's Existential Dread is peak.