The X-com series. Some of my favourite games ever are X-com apocalypse, X-com terror from the deep (I like the lovecraftian themes they include)
System shock I and II. Very hackerish, they might be old games, but the gameplay is superb.
Doom 3 is a new favourite of mine. As well as half-life is another favourite, submarine titans. And of course the old doom games. I hear a new X-com game is in the pipeline, this time a FPS.
Anyone play Blood, or blood 2? the dark humour and bloody violence is quite amusing. And of course any game that allows one to pitchfork someone to death, or set them on fire with a lighter and a can of hairspray is a hit with me. And of course, watching some bugger get set on fire, or blown to pieces with a flare gun to the face is bound to crack me up