I've been playing through the single player campaign for "Rainbow Six Vegas" lately. I'm hoping to finish it before the sequel hits the stores. Yes, I've preordered it.
I seem to do a little better with the slower and more thoughtful pacing of R6 Vegas, when compared to the spawn-sprint-die, spawn-sprint-die pacing of Call of Duty 4. I haven't played multiplayer against other people all that much, though, so that could be a mistaken assumption. Time will tell.