For me, the most important element in a game is immersion: I play in order to forget the real world for a while, and live inside game. This could mean a story with surprising twists, exploration of richly detailed universes, a satisfying set of puzzles, wonderful graphics and atmosphere, or a progression of skills with delightful effects. I really enjoy creative, conceptual indie games.

That means that I usually dislike multiplayer games: nothing can ruin immersion like an immature player. Ugh.

Also, I have low tolerance for frustration, so games that are repetitively very hard tend to annoy me. This also means that I enjoy casual games! I've played through almost all the casual point-and-click and hidden-object games available on Steam, and have written many reviews of them.

I play on Linux when possible, also using Steam installed in CrossOver (WINE): you'd be surprised how many games just work. Unfortunately, I still need to reboot into "GameOS" to play many games.

I have an NVIDIA 3D Vision kit, and it's really great for the few games that support it well! It's one more way to get immersed.