An unfair comparison in my opinion. As others have mentioned Halo does 4 player co-op and places it's emphasis on wide open environments as opposed to Killzone 2's more restricted and linear gameplay, which allows for better visuals, given that it's more limited.
Killzone 2 was developed as a technical showcase, and it shows. It's an absolute monster in the graphics department, and despite being out for nearly a year, not much has come close. I'm actually still not sure if Uncharted 2 really does surpass it.
While Halo Reach might be in it's Alpha Stage I sincerely doubt it will be able to match KZ2's visuals, simply becuase it's a different engine focusing on different strengths.








