Watch Hedon from TekAdvisor on www.twitch.tv
Hedon's a Standalone Adventure game using the GZDoom Engine. It's not to say that it's not a competent FPS, but expect a fair amount of platforming and world building.
Watch A Boy And His Barrel from TekAdvisor on www.twitch.tv
One of the most humorous mods I've tried in a while, it combines Doom with the "Companion Cube" section of Portal with great success, and now it has more custom levels to showcase the new game mechanics.
Watch Umbra of Fate from TekAdvisor on www.twitch.tv
Unbra of Fate was thoroughly impressive, oozing with style and taking advantage of GZDoom's features to create a challenging and atmospheric experience.