I'll give it a 9 out of 10.
It's a great game, the gameplay is excellent, everything has been already said about the graphics and the MP is just incredible, better then say MW.
On the other side the SP was too linear, and didnt offer enough variety.
Overall: Great game, not far from being one of the defining games of this generation. Let's see if GG can pull it off with KZ3.

9 out of 10, singleplayer wasn't the greatest thing I've ever seen, yet the overal feeling and atmosphere were great, multiplayer is awesome

9/10
+ visuals
+ online
- no coop or split screen

9/10 great game.

+ FPS cover system
+ Great graphics
+ Addictive multiplayer

- NPC's were boring and meaningless
- No co-op or even multiplayer on same console

8.3
+Interesting story
+Kept my full attention for one-two weeks
+Graphics

-Generic FPS (didn't truthfully bring anything so new)
-Bad Controls, made my game very sluggish
-Class System was somewhat unfair to some users
-Playing with friends was a chore
-New DLC wasn't that great

8.5
+ good storyline I thought the length was ok for a FPS
+ online was pretty fun with tons of support from the makers
+ graphics were insane
- the online community sucked
- wish they would have went the route of what resistance 2 did with the co-op mode.

I like how so many people are saying KZ2 didn't bring anything new to FPS gaming when KZ2 easily has the best AI of any FPS, it sets a new standard as far as I'm concerned, and the AI is the only reason I enjoyed the single-player campaign. In fact, the main reason I bought the game was because of the videos for the AI, I wasn't planning on buying it until I saw this video:

There isn't a game out there that does AI anything like this. Also ironic since a lot of people are busting a nut over a recent generic FPS. :)

6.5/10 based on single player

+ Controls. I actually enjoyed the weighty controls and the lack of autoaim.
+ Enemy design. Some helgast are pretty cool.
+ Mech section was well done.

- Weak campaign. Very few parts that stick out.
- Bad AI. Most enemies could be defeated by rushing them with melee while in cover.
- Way too few opportunities to use the sniper rifle.
- Exploding barrels. Man I wish game developers would stop it with these.

- Extremely useless friendly AI. Rico was the most useless piece of crap during the last fight.

Yes, I found the AI to be bad. I played on hard and they were still dumb most of the time. Rushing proved to be the best strategy I could find as it left enemies confused.

I played Killzone 2 multiplayer, but not enough to form an opinion on it so I excluded it. I'm sure that's the strong point of the game, but it didn't really click with me.

More like the AI was so good the only way you could advance was to take advantage of the most boring way to play.  I don't think I ever knife-rushed on Veteran unless there was only one enemy left. You died almost instantly after leaving cover on Veteran, the only times I manipulated the AI was to beat the final level because, to be honest, I was too noob to beat it legitimately.