COD4 was great but in my opinion only in single-player.
They ruined the multiplayer in COD4 on the Xbox360 by having a forced radar where everybody can see everybody at all times! What's the fun in seeing all the enemies on your radar, and they can see all of you?
I mean, it's supposed to be a more "realistic" game and all, but in what actual combat/warfare do you have a "radar" available that shows ALL the enemies' positions at all times so you can just walk over and pick them out?
(On the pc version of COD4, this all-players-visible radar can be disabled though).
It's why I much rather play COD3 over COD4 multiplayer any day.
/COD4 vent..
Anyway - I look forward to L4D2 this fall. Hope they improve the graphics a bit too, as L4D looked a bit dated with the old CS engine.