It could've been better, but I would definitely never vote this for Game of the Year. Simply put, over hyped.
Singleplayer was great, although short. Way too short. Average, each mission took around 10-15 minutes ON HARDENED. Veteran took 20-30. But, good gameplay in singleplayer (bad story though). Spec Ops was definitely good. But, considering how IGN and Gamespot themselves stated that in Spec Ops, you were "going to be pitted against Infinity Ward's imagination" didn't live up to that. Instead, you repeat repetitive missions over a variety of locales. Who wants to defend a base in thirty different locations? Me!!!!
Multiplayer isn't all that good either. It's a pick up and play game, and anyone can be good. In fact, I committed suicide a bunch of times in a match and still got EXP for it. It's all the same really, just with different guns. Kill streaks are now extremely overpowered (especially with people camping for a nuke). And all you're doing is just killing. No variety whatsoever. I liked the semi-complicated maps in COD4, but now, like WaW, everything is uber-simple.
It'll be good for a while, but if you want an expansive game, go look somewhere else. This isn't just the legend that COD4 used to be. I suggest Bad Company 2, MAG (if you're on PS3), flowER (if you're on PS3), Bioshock 2 (if it's good), AVP, or the next COD, which hopefully, might be good.
Psst, psst, it's set in Vietnam, created by Treyarch, and after WaW, expect lots of gore, blood, and Communist Zombies mode.