I can't say much about the single player as I have not really played it. much but the AI didn't not seam that smart!
But multiplay and the frontline HD is worth the buy, I believe the multiplay is made by a different company and it shows!! Its alot better than the last COD's multiplayer versions. As it is alot harder to play, graphics also better! This is not a game for under 16 COD is! no spray and pray, you need to know your weapon well.
People might think I have a problem with COD but I love it, I have had every COD since the first on PC! But I Just can't stand people saying this game is no good because its not like COD.