There's been a lot of backlash against this game, and I'm not really positive why. Bottom line is if you like Call of Duty games, you'll like this. It's got everything you'd expect: Over the top single player, variety of weapons and levels, and an addictive multiplayer. And zombies.
The single player game is maybe not as strong as far as gameplay goes as it's predecessor, Modern Warfare 2, but it's not quite on the same grand scale. However, as far as characters and story go, this is probably the best Call of Duty campaign of the whole series. The game has numerous twists and turns you won't see coming, and it all comes to a satisfying conclusion. I don't want to talk too much about the story as to avoid spoiling it. Also, the varied time periods and player characters keep the game very interesting. The voice acting, featuring Sam Worthington, Ed Harris and Gary Oldman is also very strong.
The multiplayer has been overhauled from Modern Warfare 2, and some of the changes are great, others not so much. Instead of completing challenges to upgrade your guns and equipment, there is now an in game currency used for customization. This is great as you can pick and choose what weapons and upgrades you get and in what order, but it's not quite as exciting as the old system. "3 more kills and I get the tactical knife" is much more interesting than "3 more kills and I get a couple of hundred call of duty points." Still, it works, and is very addictive. The addition of wager matches, where you play customized shooting games modes to win points (or lose them) is very exciting and having these modes to play games as alternatives to standard modes adds a lot of life to the game.
Zombie mode is a lot of fun, if too similar to the mode in World at War. It's a great time with friends, but solo zombies is a little flat. This game really could have used a Special Ops mode like Modern Warfare 2, as that could be a lot of fun alone.
Overall I'd recommend it if you like Call of Duty games or other fast paced action shooters. There's nothing revolutionary, but there's lots of fun to be had.