I've played all the Modern Warfare games. However, none compare to what Treyarch has done to the Call of Duty series.
The Campaign is arguably one of the best stories I've heard in a video game. It all consists of a guy who's being interrogated and is forced to remember his past. The majority of the gameplay is played in flashbacks, which I've never really seen before. I will leave it at that so I don't spoil anything else.
Multiplayer, the maps, the weapons. It's everything Modern Warfare should have been. There is something for everyone. The weapon selection is top notch. The gun stats are all balanced quite well. The best part about multiplayer is that it's at a slightly slower pace than Modern Warfare, meaning your reaction time doesn't have to be absolutely perfect when two people from opposite teams fight for a kill. Killstreaks are also a blast (pun intended).
Zombies mode is also a nice addition. I just wished all the maps came with the game, and that you didn't have to pay for the other ones.
My favorite Call of Duty game, and it doesn't disappoint me in the slightest. I give it a 9 out of 10.