Right now, Modern Warfare 3 is sitting quite high on Metacritic at a very solid 89. In the 5 days since its release, MW3 has been subject to extreme amounts of praise and criticism, and I'm going to offer up my two cents on it.
So far, the story line in the Modern Warfare series has been so-so. It hasn't been nearly on par with story based game series like Mass Effect or Assassin's Creed, but it hasn't been terrible. What it has been, in one word, is 'forgettable.' The only parts remembered to this day from CoD4 and MW2 are the very, very cool parts, and the very, very challenging. Do you remember the nuke going off in CoD4? Or sneaking through a field of enemies? Or No Fighting in the F-ing War Room? Of course you do. But do you remember 'The Bog,' 'Heat,' or 'All In?' Probably not.
MW3 is about as easy as MW2, which is to say, very easy. I was able to beat MW2 on veteran in less time than it took to be beat 'Charlie Don't Surf,' 'One Shot-One Kill,' and 'No Fighting' on veteran. MW3 also has very few parts of the mediocre story line which are memorable, excluding a couple of really cool plot twists.
Spec Ops and Survival:
Spec Ops is very similar to spec ops from MW2, but with different missions. Not much to say here.
Survival is new to the MW series, and is actually a lot of fun. You might be tempted to think of it as Nazi Zombies, but the enemies have guns, but don't look at it like this. It's its own thing, with it's own play style. It does have a level system to it, so will have to invest a fair amount of time to unlock everything, but you'll be glad you did.
This is the hard part; how do you classify a game like Modern Warfare 3? If this was your first ever video game, it'd be the greatest thing you'd ever experienced. However, having played a large amount of video games, I'm disappointed with MW3, though not as much as I was with MW2.
On its own, Modern Warfare 3 is an absolutely fantastic game, very close to a perfect score. Compared to the massive innovation made by CoD 4, and the varied additions Treyarch has made to the series, MW3 is average. It doesn't add to the series, but it refines it.
I very much recommend renting it first, or playing it at a friend's house first, and if you really enjoy it, but it. If you're looking for a lot of innovation or a great story, skip it.
If you're looking for a number: 8.5 out of 10