http://doom.chaosforge.org/ I had a quick look at this a few months ago, back when it was ASCII only, and couldn't get into it. They've now added graphics(!), and it's a hell of a lot of fun. Not the deepest roguelike, possibly, but there's some complexities to the combat system where if you run around and sidestep in between shots, they're less likely to hit you. Emptying your pistol clips into demons as they charge towards you while 90s metal plays in the background is an experience not to be missed.