I do alright, better in single player than multiplayer, but it has been a while since I played against anyone other than brain damaged Halo pwners (also known as my only gaming friends.)
I don't play online anymore, so I have no real frame of reference, but whenever I play against my friends, I always win (and I mean always, often going through matches without getting a single scratch while I take them all out.) I can switch tactics easily if someone's managed to figure out what I'm doing, and given even a few seconds I'm a crack shot on most games.
Generally nowadays I play L4D 1+2, some Halo, and then whatever my friends are playing, so CoD 4, Medal of Honour. They like the war games, I like the sci-fi. I own them in all of them.
EDIT: Oh, and the reason I say I'm a good player despite not playing anyone new is because all of these games I can complete on the hardest difficulty settings, so even though it's easier versus computer than a good normal player, I still figure I must be doing okay to win on the hardest difficulty.