You'll be playing it for a very, very long time.
An absolute BLAST to play online, which for the most part feels quite balanced (grenade launchers feel incredibly cheap). There are a few glitches with the partying and lobbying system that can be quite annoying, such as your party (all or some) not coming with if when you host, and not being able to join a person's lobby period until multiple invites are accepted. They aren't game breaking or of too much annoyance however, as my 12 hour play marathons can tell you.
The single player campaign is short but also of very high quality. The difficulty can be pretty intense at some parts, and can be quite frustrating and somewhat monotonous at times, but overall it excels at top notch standards and has a very gripping and interesting storyline.
Graphics: 9.5
Some of the best graphics around for sure. For the most part it's not visually eye exploding (don't get me wrong it looks great), but considering the amount of stuff happening on screen, and that the game runs at 60 frames per second, it is quite the technical achievement. It loses some points as I just said for not being completely mindblowing by the naked eye, but also for a few frame dips in the single player campaign.
Sound: 9.0
Not really anything out of the ordinary here, but it's hard for me to really fault the game for that. All the guns sound great (about how you'd expect), and the voice acting, what there is, is fairly top notch. It's all quality here, but still nothing you'd write home about.
Replayability: 10
Man oh man is there a lot of replay value in this sucker. The single player not so much (because it's very short; about 4-6 hours on normal), but you can definitely tell that Infinity Ward put a TON of time into making their multiplayer component the best that they possible could. On top of the 16 multiplayer maps and a dozen or so game types, the thing that really gives this game legs is the ranking and challenge system. Every match you play you get experience points depending on how you as an individual (and as a team) did during the match. As you raise your military ranks up higher and higher, you'll unlock new weapons, perks, and challenges.
Challenges allow you to complete little missions within your matches that net you experience and items such as customizations for your weapons. It's not as simple as just unlocking say an M4 and having all the fixings right away; you must EARN your sights and camouflages for each by doing things such as "get 100 kills" or "get 50 headshots", etc.
As for the perk system, you are allowed to have three of these enabled at all times on your character, grouped into different categories (for balance), and they do things for you such as let you do extra damage with your weapon, let you carry an extra primary weapon (instead of a pistol), let you hear the enemy team voice chat in proximity, allow you to carry an RPG launcher, and more.
There is a ton of customization for your soldier, coupled with the fact that this in of itself becomes EXTREMELY addicting, and adding the fact that the multiplayer is also EXTREMELY addicting and fun, you'll be playing it for a very, very long time.
The single player is very short as previously mentioned, and probably won't have you coming back very much, but what is there is very good and let's face it folks, where it's at with this game is the multiplayer. If you aren't into online gaming, this could be the game that changes your mind.
Overall Average: 9.5