I've been playing this game since it first came out, but I had only been playing multiplayer and zombie modes up until last night when I finally beat the campaign mode. First, I know the two zombie modes get a lot of attention and they are entertaining, but I wouldn't consider it long lasting fun. It really just feels like a little break if you are either tired or frustrated with multiplayer (maybe you got owned 3 maps in a row). Both zombie modes are pretty fun, I do like the addition of the arcade mode. But it is just horde mode from Gears.
Multiplayer is, of course, where the game really shines. Multiplayer is fantastic. I would say it is better than Modern Warfare 2, but I think it really only feels better because I was ready for a new game and a change. Trying to look at them overall, I would say they are equal. Now the maps really do feel better to me. I find them to be a great mix of size and layout. The maps feel more intense to me. I can get into the action within a few turns after respawning. I also remember in MW2 that I could always find places to hide for a minute to be safe, but these maps have less spots and I find myself in more intense battles. One change I would like to see is that the RC car becomes less powerful, easy to kill, or a higher kill streak requirement. My main complaint for this is because that damn thing kills me every freaking time. I swear to all that is holy every time I hear an RC car followed by the stupid voice saying one has been spotted in my area, that damn things kills me.
Campaign mode feels like the offspring of a menage-a-trois involving Modern Warfare 2, Assassin's Creed, and Fight Club. I had a blast playing it and the story wasn't too bad even though I didn't quite grasp some parts of the story, but I'm not the smartest peanut in the turd. The character you play has to be the most bad ass soldier ever. I got knocked out and captured and threatened to be killed a few too many times. It did offer about 4 hours of play time, but I did do the easy mode mainly because I wanted to beat it. I didn't buy this game for single player so I just wanted to get through it so I could see the story.
Overall, awesome game. I am even more impressed since I always had a bad impression from Treyarch. However, I think they have really outdone themselves. I am going to continue enjoying this game, especially since there is a growing concern that the next version of CoD could be a monthly pay model and at that point, I am most likely out.