Well the difference in sales can be chalked up to both a larger install base on the 360, and the fact that Microsoft cornered the high end demographic early on in this generation. Which means that not only are there more users to buy, but they are also more apt to buy. Then as if to add salt to the wound Halo is a convergence in Live. It is a constant between most libraries. Making it almost a requirement.

Speaking to the difference in reviews. I think the exclusivity of Killzone 2 probably actually helps its review score. Reviewers do have to take into account console user specificity in reviewing. Knowing that a PS3 owner has no option to play Halo, Left 4 Dead, or a solid Orange Box. They must give the game a slight bonus in light of the offerings. So it isn't going head to head as much as it is colliding at an angle. Were Halo 3 on the PS3 the reviews for Killzone 2 would in the end probably be lower, but on the upside the sales would be higher.

Halo 3 is the gold standard, inventive, original, dynamic, and crammed with features. All of this with obscene balance testing. Not to mention the cult like following it garners from gamers. Quite literally you can play the game for a year without even touching half the offering. It really isn't a matter of preference you have to stand in awe of the craftsmanship involved. Don't take my word for it though go play Halo 3 for a few hours. Every game you play is entirely different just the limitless strategy is impressive.

its because halo is a ten times bigger ip than killzone. no matter how good killzone is it will never match halo sales popularity.

regarding actual game in hand, halo is a fan favourite, and is massivly overhyped, therefore reviews will just give it 10`s across the board. although it is a very good game.

Halo 3 has a lot more to offer than KZ2.

Why does Final Fantasy X have a higher rating than Mana Khemia? Why does Mario 64 have a better rating than Spider Man 3? The answer is simply they are betterr games.

I believe the kill in killzone killed it sale, if your kid ask you for halo 3 you'll buy it because it doesn't sound to violent but killzone the name itself sound violent

Halo sounds religious.

This^

What?

You clearly started your comment with the assumption that sales and ratings equal quality.

If you expect some answer like "the reviewers were biased", or "Killzone 2 was too hardcore for the masses", what is the point of caring about the ratings, to begin with? 

There are only two possible interpretations:

1. Quality is subjective, ratings and sales don't mean anything at all, and this thread is useless.

2. Ratings are Teh Truth, the reviewers are Ultimate Grandmasters of Gaming, therefore Halo 3 is just better, and this thread is useless.

Co-op this co-op that... Co-op does nothing for me. I don't need it. I played the first Halo and didn't enjoy it. Nothing will make me want to try the rest.. However, Killzone 2 is a beautiful game.

Play them bother and form your own opinions.

I enjoyed both campaigns but personally prefer the KZ2 MP by far.