I think reviews are indeed broken, but just the other way around:
The game is probably way overrated.
Thing is: Halo Reach is very similar to GTA IV - a game so hyped that hardly any game reviewer even considered giving a score less than 90%, because with all the hype you know every reviewer will give ridiculous high scores, and it always looks strange if your score is completely different than that of all the other reviews.
Lots of gamers however soon expressed criticism and complained that the game is way overrated. Now the review score of GTA IV on metacritic is 98, the user score however is less than 80.
Halo 3 is similar: Metacritic review score 94, metacritic user score 76. And Halo Reach will probably be similar as well. If a game is extremely hyped for like GTA IV, the Halo series or GT5, then review scores are usually overrated.