PC Magazine takes issue with a few flaws in Halo 3; the Arbiter's seeming invulnerability and the enemy AI's inability to see you coming (what difficulty did they play at?) bothered them. Nothing positive, in particular, seemed to stand out for them:

It's not the best looking Xbox 360 game (Gears of War has its number, there), and it certainly doesn't have the best story (BioShock), but Halo's (and Bungie's) skills lie in synthesizing all of the above to produce games with maximum appeal and minimal compromise.

They seem to grudgingly give the game a score of 85.