Psychophobia is a Doom II mod which can be played with gzdoom and skulltag. Features: new weapons, new monsters, new textures, new music, new sounds, new decorates, new Hud, new maps, and many other different things.
I really enjoyed the level design and weapons.
It's like a ton of different weapons and enemies thrown together in a really coherent way that's really fun to play just like Brutal DooM.
There's almost no logic behind some of it, but it actually works really well. There are space marines from Aliens mixed with UAC marines, cultists from Blood, new Doom demons, hexen enemies, quake 2 etc...
The level design offers a great balance of aesthetics, exploration, and fighting for your survival using an awesome variety of weapons against hordes of demons.