Finally, which one is the best : Gears of war 2, Killzone 2 or maybe Halo 3 ?

Final Fantasy Tactics.

Killzone 2.
Hands down.

This thread is not for RPG lovers ( but I agree Tactics rock... )

The one where you play a stupid main character who kills waves of similar-looking enemies with guns.

Well I haven't played KZ2 so can't comment on it yet but on the two I have played definitely Halo 3 and the Halo series in general. If I had to take a guess of how I'd be affected by KZ2 if I played it, I doubt it would go as high up as my liking for Halo 3 or possibly even Gears 2.

i hate to do this to my ps3 fans but im a TPS guy so its Gears for me although i dont own the game or a 360 i have played the 1st one and i liked it

gearz is the best tps and kz2 is the best fps...

...halo is the best halo fps :p

Best what??? best game? if it is then it's a matter of opinion.