I have PD:Z, CoD2, PGR3. I've played King Kong.
Perfect Dark: Zero
I LOVE this game, the graphics are good, not perfect, but still, I love this game. I have noticed one short instance of slow down. However, the action really makes up for the small shortcomings.
Call of Duty 2
I haven't played much of this game yet. From what I have played, the game is amazing. Graphics, gameplay, playing on Live, everything is more than what I expected. Great Game.
PGR3
Graphics are the best I've ever seen in a racing game. BEAUTIFUL graphics, no slowdown at all. Whatsoever. Great cars, great tracks. Just all out perfection. Best racing game since Need for Speed 2 and Need for Speed: High Stakes (in my opinion, as you can tell, I loved those games). Racing a McLaren F1LM and a CLK-GTR side by side across the Brooklyn Bridge is breathtaking. It has a really cool arcade feel to the game, but still a bit of simulation.
King Kong
I only played a demo of this game, but its definetly the next game I'm going to get. Graphics are so good they make me wanna cry. Kicking the crap outta a T-Rex with Kong is just so friggin kewl.
My favorite all around game so far is PD:Z, closely followed by PGR3. Its a good sign if I haven't played a game that I love.