I've heard ALOT of people complaining about the aiming, but I honestly can't say that I'm having any problems with it. There's a ton of people on killzone .com askin for the next patch to fix aiming.
I've beaten the game on the harderst difficulty already (ok, the hardest you can start on, not Elite which I've just unlocked) and I got all the speedkill trophies for each boss. lol the last one was under 20 mins, who wouldn't be able to get that one? And online I'm killin people just as effectively as I used to in COD4. A couple of 40+ kill matches there with less than 10 deaths.
I hope they don't listen to the whiners and patch the game, it runs fine. And if you're findin it takes too many bullets to down someone, crouch, it increases accuracy, use only burst fire to reduce recoil in-acuracy and also aim for the head cause one shot is enough (unless you hit their helmet, then it takes 2 shots)
