I have all 3, and I will get Killzone. The controls are different, and I think they definitely will take some time to get used to. It'll be the first game I purchase for my PS3.
Controls matter to many people. I know my played the RE5 demo and didn't like the controls, so he is skipping the game. If you don't like the weighted feel of Killzone 2, there's no point in getting it. It's a shooter, and the most important part is how it feels when you control it. I'll probably play COD4 multiplayer more than I play Killzone 2 multiplayer.
Threads of Interest:
The Movie Thread: http://www.vgchartz.com/forum/thread.php?id=6880
The Crow Eating Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=3886
The Betting Thread: http://www.vgchartz.com/forum/thread.php?start=0&id=7104
Custom GIFs Thread: http://www.vgchartz.com/forum/thread.php?id=18963
The Greatest Game Ever Conceived On Any Platform
Tag: "I have tasted Obi-Wan's bitter tears"
