Typically, it's been either RTS or RPG for me. What I really love in a game, though, is a good plotline, great characters, and a vast and interesting world that had a lot of creative effort put into it. In fact, I normally value the world more than the game play. Beyond Good and Evil for instance.
If I had to choose by game play, I would say first person and RTS. Things like Rise of Nations, Stronghold, Lost Kingdoms, a few turn-based first person like LoTR: The Third Age, Final Fantasy: Crystal Chronicles, Pikmin, city building games like the ones from Sierra. I'm thinking about trying Elderscrolls again.
I also love MMORPG's, although I don't play them much anymore. I'm not willing to pay monthly fees and the server quality of the free ones like Silkroad and Kal is horrible. However, when I have less on my plate, I
might purchase a month from WoW just because a lot of my friends play it and it's damn fun.
I also have a soft spot for rythym games. Really, just Stepmania.
