Over the years I've played every genre conceivable, but depending on the amount of free time and mood, my preferences are such:
1. TBS For when I have the most free time available... delivers the most satisfaction in the long run than any other game genre, offering the greatest challenges and longevity, IMHO.
Current favourites: Galactic Civilizations II /DL/DA/TotA, Age of Wonders: Shadow Magic, Disciples II (but I think I most prefer the "4x" empire building games the most, such as the GalCiv series and others).
2. FPS Short on free time, for when I just want to jump in and out and have fun... mostly for stress relief, although this category can be subdivded: pure action, tactical, rpg or in current trends of the genre, a blending of all three elements.
Current favourites: Counter-Strike: Source, Far Cry, Unreal Tournament.
3. RPG Although there is a "role playing element" to most games, I guess I prefer the terms "class" or "character" development which involve some sort of skill upgrading or unlocking and a decision making process by the protagonist (but not always) affecting the path or outcome of the story.
Current favourites: Deus Ex, Vampire The Masquerade: Bloodlines, Fallout 2.
That's it for the most part.
My interest still leans heavily toward the 4x empire building category... best bang for the buck me thinks! 
