Putrefier

A single GZDoom map for Doom 2, not only raises the bar but megablasts it up to "how the hell is that even possible?" heights. Putrefier is set in an imposing UAC facility filled with shadows, beasties, and architecture straight out of an idTech 3 game. As you descend into the base, things get weirder, with creepy malfunctioning technology and demonic spaghetti crawling out of the walls in a sickeningly cool manner. There are no fanciful scripted cutscenes, but the thick atmosphere of the map suggests that the experience is part of a larger narrative than what's visible on the surface (a notion heavily reinforced by the set-up to a brilliantly-done boss battle).