BackFire
Blood. It's nature's lube
http://www.gameinformer.com/NR/exeres/41497688-5BCB-4C0A-B952-A1B1440E2139.htm?CS_pid=200224
Both the main review and the second opinion are 10's for Bioshock. While the main review is a 9.5 for Metroid, and the second opinion is an 8.75.
It's not when the game is released, it's when the publishers send the magazine the games. They got Bioshock a good while before the release date and thus were able to publish their review earlier. Nintendo didn't send out Metroid until later, so print magazines had to wait on reviewing them. Heck, EGM is just reveiwing the game now in this comming issue.
Again, if you don't believe go look on Gameinformer.com. You can look up reviews based on what issue they were published.
When a magazine chooses a game of the month, it's out of the games reviewed in that issue, not necessarily out of the games coming out in a given month. Since Metroid and Bioshock were both reviewed in different issues they were not in competition with eachother.
Though it's clear that had they been, Bioshock would have won.