The only ps3 game I've ever stuck with for a long period of time online is Resistance:Fall of Man.
No other FPS comes close imo. I can't stick with games like MW2 and BFBC2 (even though I loved it)
I'll give Uncharted a go soon, see what all the fuss is about.
Resistance is also a great Multi player game. Games like MW2 are far too noob friendly. Its basically who sees who first wins, which creates camping and really boring games. Basically just wait for some one to run past you and cap them because they have no chance of turning around and out gunning you.
Uncharted is much more fast paced and arcadey. If a bad player is shooting you from behind, you can just spin around and still out gun him, its great.
I hope killzone 3 is good, the sluggish controls ruined the second one.