In COD MW2, they made it so even if you suck really bad you can get kills, which was not the case in COD4. Auto Aim, Heartbeat Sensors, Thermal. In Killzone 2, you get kills based on your tactics, and skill. Which you may be better at, or worse at. I wish MW2 didn't have auto aim, but hey what can I do.

Yea he pretty much summed it up, Killzone 2 takes more skill, I see alot of people getting only 3 kills and 16 deaths or somewhere around there.

Your tactics greatly determine how many Kills/Deaths you will get, running and gunning doesn't really cut it for most people.

if cod6 is anything like cod4, then killzone is just a lot more tactical. You have to use your head more. The multiplayer in the kz2 is extremely satisfying though. Atleast in my opinion.

Killzone 2 is a strategy shooter, a simple one.
MW2 is basically a run and gun shooter, with hundreds of custom-izable parts which makes the replay value much more then the regular FPS

kz2 dedicated server network is wonderful. MW2's network is total garbage.
In kz2 you can select a "my rank only" game to eliminate being the noob in a lobby of long time players.]
Also, a single tactitian class can keep the spawn camping down by figuring out good places to put the spawn point.
Kz2 takes more skill and is more action packed. There are way too many campers and people who hide in corners in mw2.