doom like zdoom or whatever its called, its really fun and loading up insane .wad files is a blast.
i play angband every now and then, then i get frustrated and delete it.
i'm not playing deus ex since i beat it about 4 times, after which it got repetitive. the mob's behaviour is very strict, they will always move the same exact way down to the pixel, so you just get gun, shoot, win.
(also, that jump speedrun on youtube kinda ruined it for me...)
i'll gladly play stalker once every otehr year.
i also play quake 3 in the quakelive incarnation;
and freecell ofc.
i went crazy a couple years back and ran through *all* the lucasarts games, like day of the tentacle, monkey island, beneath a steel sky ..
the new C&C95 game is ok if you take off all the "new" options and overlook one or two bugs.
i also played the original thief 1 tnx to the people on this forum, loved it.