Super Mario 64 Splitscreen is a multiplayer mod that is implemented well enough to make it almost feel like a natural part of the experience.
Serious Duke 3D is a mod for Serious Sam 3 that recreates a chunk of levels from Duke Nukem 3D and the result is phenomenal.
Warhammer: The End Times – Vermintide is a solid game with brutal and satisfying combat that’s best enjoyed with friends. It’s also a great take on the Left 4 Dead formula.
Slayer’s Testaments is a Quake mod that successfully captures the gameplay and spirit of Doom. It’s just a little rough around the edges at the moment.
Hideous Destructor turns Doom into a slow-paced tactical experience. The gameplay is challenging but feels rewarding and only those with patience will survive.
Complex Doom offers a more challenging Doom experience complete with new weapons, enemies, and an inventory system.
SIGIL is a claustrophobic and challenging megawad for the original Doom accompanied by awesome music composed by Buckethead.
Brutal Doom and Project Brutality take the Classic Doom gameplay and modernize it, amplify it, and offer a more intense experience.
Quake 4 puts you back in the war against the Strogg and this time you take the fight to their home planet.