A couple of people pointed me to a great post, by Gabe of Penny Arcade, about a problem professional reviewers are likely to run into when reviewing sandbox games. The gist is that sandbox games are not designed to be played through quickly or in a linear fashion, so a review of a such a game is not likely to be accurate unless the reviewer has the time to play the game as most gamers would play it: leisurely.
I think there's more to consider when reviewing sandbox games than just the time constraints, but I'll save that for later. For now, I want to re-emphasize something I said in response to one of Brian Green's articles. Basically, I think there's little sense in any game's review coinciding with its release date. Short delays in getting games reviewed are really not a big loss to developers, reviewers, or fans.
Who are reviews really for?
I'm not sure, but I bet that most people who read any type of gaming coverage at all read game previews. And odds are that a gamer who hasn't been hooked by a game's previews isn't going to pay much heed to the game's reviews. That gamer has probably gotten into the habit of glossing over any news about the game, so it would take an extraordinary marketing stunt to get him or her looking again with an open mind.
If the gamer is on-the-fence and waiting for reviews to tip him one way or the other, he's probably already skeptical and therefore more open to non-professional reviews than to professional reviews.
Reviews probably make a bigger difference with non-gamer gift-givers, like parents, and very-occasional gamers than with regular gamers. These are the people who are in the most need of when help making a purchasing decision. Even then, such consumers are more likely to simply ask an offline friend or store clerk about the game than to look up a review on a website they probably haven't even heard of.
Reviews probably have a more significant effect in influencing delayed purchasing decisions than purchases on release day or even within the first week of release. Reviewers, please don't feel rushed. Marketing folks, relax!