So so. Frankly, there are a lot better gamers out there than me and heck, even some non-gamers can kick my arse at certain games. Going by genres:
It's hard to tell whether one's good at something like RPGs. Morrowind/Oblivion I kicked arse, but then, I'm pretty sure the game's designed for it. Dragon Age: Origins I played through on Normal, found it remarkably easy after a while, but that's likely cause I stacked Mages (3+warrior tank). I played ME2 on some higher difficulty but couldn't tell you exactly which one, I was aiming for the highest, but I might've tuned it down to the one below. But yeah, I reckon I'm above average at RPGs.
Third person shooters I'm generally great at, at least the singleplayer. Likely has something to do with the fact they're (well, the ones I play) mostly stealth games or at least have stealth elements and that's definitely my forte and my preferred style of play - I like having the time to think and plan.
FPS... Well, I played CoD on the highest difficulty. Bit of a pita getting pwned now and again by ridiculous difficulty, but mostly managed through it fine. Multiplayer... I was relatively decent at Counter Strike back when I played it, but nothing special (I suck arse now), never really played CoD online (once, for some 5 minutes, when it was a free Steam weekend but I got bored, not my kind of game). Battlefield was always my (FPS) game and I do pretty well at it with most roles, particularly vehicles (further particularly air vehicles, whether doing transport, assault or both), but I also do just fine with infantry as well, mostly playing snipers and engineers as I enjoy support, but I play Medics and to a slightly lesser extent, Assault as well.
RTSs I'm generally not good at. Could be just lack of my love for the genre, I do enjoy it on a level, but never really played it much. C&C Generals: Zero Hour I fire up with some mates now and again at LAN parties, but I'm awful if I need to be alone. With a team mate? Gimme a bit of protection and you'll have a pile of Auroras ready to blast the hell out of whatever you need as well as a pretty good protection. So all around, I'm a decent support, but I wouldn't survive 5 minutes with guys who played any RTS regularly. As for TBSs, I like Civilization and TW: Rome, but can't really say I was ever especially great at them.
MMOs... Long story short, I'm good at them. I've got pretty decent organizational skills (that mostly really come down to dedication), so I usually move up as well and end up leading the others and have no trouble playing my role to the max while doing it.