Not a big fan of Killzone 2. I couldn't get over its controls mainly.
But other than that, the one thing I give credit to it is its "heaviness". You really get a sense of power and impact when you shoot a Helghast in the head, or the body (and seem them react by writhing left and right).
The game also had a very tactical feel to it. Cover was an absolute must and you really needed to focus on flanking the enemy.
These are the things that I felt KZ3 lacked.









