I played the PC version as well. I thought it was really good, but the "game of the year" hype was a little overdone. As good as it is, and every FPS lover needs to play it, I didn't feel the same way with COD4 that I did during the Half Life 2 games or Bioshock. And I thought Team Fortress 2 was a better multiplayer experience. Still a great game, though.
I'm not sure I agree about the too short comments. When I finish a game without that "Isn't this damn thing almost over" feeling, I'd call it a success. I've wasted too much time finishing games that have stopped being fun, just because I had too much invested in it, to ever complain about a game that left me wanting more. I would always rather have a short game with well chosen levels than an extra three hours of mediocre or repetitive gameplay that adds nothing, and is only there to meet that magical 8-12 hour mark.