What I like

Major genres and what I like.

FPS: Second on my list of what to get.
Just had to get the major one out of the way. They're fun, but most of the time they don't scratch that itch I get. I want some huge, overarching game that seems to mean something, and you just don't get that in most FPSes. The multiplayer for the best ones is really good, though.
P.S. just put Third person shooters in here too, they're not that different.

RPG: What I live for.
Ah, here we go. I like western RPGs and JRPGs, but the latter hasn't been winning any points with me lately. I liked the old systems, when it was turn based and you could actually tell everyone what to do. I used to like traditional RPGs like Neverwinter Nights 2, (More recently, Dragon Age: Origins) but my taste for them seems to be spoiled by my absolute favorite games- Action RPGs. The open-world ones (TY, Bethesda) are pretty good, (scratch that, awesome!) but I need more of a reason to explore. So, that pretty much leaves Mass Effect and Bioshock. Haven't played the latter, just happened to get ME1 first... and ME is awesome. Will get Bioshock, though. I just love the stories.

Action: When I see a game that catches my eye.
Pure action games are a lot more single-minded in what makes them work. If you have a good combat mechanic, you have at least a decent game, and if you don't... well, that's not a good thing. I like playing them, but I'm not going to dump a couple hundred hours into it like I could a good multiplayer FPS or a good RPG.

RTS: When the right one comes out.
Generally have cool overarching stories, and the most complex gameplay I know of. They can be hard, repetitive, or just long, but when done just right they can be amazingly fun. I tend to go for the less realistic ones like Warcraft and Starcraft. (Yes, I like Blizzard, despite my extreme lack of motivation to play WoW)

Platformers: Mario is reliably good, but other than that... dunno.
Yay for jumping on random platforms! There are pure platformers, like Mario, and then there's action platformers like Ratchet and Clank. Pure platformers are good for small doses, like half an hour at a time, with no connection to previous playing, whereas action platformers generally have more of a coherent story, where it actually might become more of an experience instead of just mindlessly jumping to the end. Not that I dislike Mario, far from it.

Sports: I'll get one occasionally. Not every year, though.
... If you like sports, get the game for that sport. (If you don't mind it ripping into shreds more often than not. Ok, I'm being uncharitable, they do a decent job nowadays.) Otherwise, don't. Simple.

P.S. BTW, my favorite compliment for a game is that it's epic. I mean this in the literal sense of the word. FPSes, are rarely epic, and the multiplayer almost never is.

Tell me any major ones I missed, and I'll talk about them, too. And remember, feel free to disagree, or give suggestions, or anything else! :)