Must have games on the PS3 are Uncharted, MGS4, LBP, Killzone 2, Resistance 1 & 2, Heavenly Sword (it is short but amazing).
Some coming are White Knight Chronicles (out in Japan and super cool), inFamous, Heavy Rain.
As for a game that is like Halo, I don't think anyone has really set out to try to replicate it or make a Halo killer. I think more developers are just working on their own franchises and trying to make them noteworthy on their inherent qualities.
Some games to stay away from are Haze and well that is really the only exclusive game I can think of that really was horrid.
If you want a Halo fix I would find a used 360 at gamestop or something they are pretty cheap now and you can get a used HD for under 60 now too I think. Best of both worlds. That is what I did and now I have all the exclusives barring the Wii because well dammit I hate gimmicks