I'm no hardcore gamer, but I am loving this game so far (only half way through, got it yesterday)
I tried playing online last night, and had a very difficult time finding matches. One point I waited for about 30 minutes for a CTF match, and never found one.
I think there is just a lack of players for this game, making it very hard to play online with.
The matches I did play were very similar to previous Quake console games, fast paced and the same types of crazy levels.
Honestly, I would recommend waiting for a more popular FPS for the 360 if you already have it on the pc.