My favorites are RTCW, CoD1&2, MoH and SoF1&2. Half-Life 1&2 are not bad either; I'm not a big fan of Doom 3, though the older ones are fun. Same with Quake 1 & 2, I don't like Quake 3, and I didn't really play Quake 4 yet. I tried FEAR and Prey, but I don't like them.