I'm genuinely surprised reviews are ranking that high (so far).
Most reviewers don't have the same tastes as I, they don't have the same expectations as I. Because they play games all day and go through such quantities, little technical or gameplay imperfections will tend to annoy them a lot simply because their tolerance threshold is lowered by the quantity of games they go through. I play maybe a game or two per month, so naturally things that I'm expecting and things that annoy me are very different from them. For example I can do with framerate drops or stutter from time to time while I can totally understand why a professional reviewer would be very annoyed by that if it's the 10th game he's trying that week.
Last but not least, the perception of professional reviewers are often affected by marketing, sponsorships, hype, free trips, invitations to private presentations, etc. Remember that article at NMA describing how the "journalists" who reviewed Oblivion didn't point out its flaws in its actual review but in later reviews of other games.
http://www.nma-fallout.com/article.php?id=37708
And really games are just like music, it's first and foremost a matter of tastes, even if 99% reviewer say Britney Spears' last record is crap, maybe I'll actually like it (not saying I do lol it's just an example). The only thing review can have a saying about that might have any validity is technical aspects ("this game has lots of bugs", "this game has an inconvenient interface", etc.) and yet again, as I said earlier, because I play much less games than them, even when their judgment strictly depicts unbiased technical aspects the actual effect of such technical aspects will probably have a much lesser impact on me than it has on them.
I remember during my first playthrough of Fallout 2 I had an inevitable game stopping bug : the non random encounter close to the beginning of the game where you meet Frank Horrigan in the Wastes wasting a guy and his family would crash to desktop. I couldn't get past that until the patch was released, and yet I still consider Fallout 2 my favorite game of all times. Had reviewers encountered the same bug and no way to fix it at the time of press release I'm sure they would have gave it a rating of 2/10 at best.
So I voted for advice from friends and demos. Nothing beats actually trying the game and deciding by myself. Or have a friend who played it already talk about it and go to his place to try it out (that's how I got into Fallout 1 DAoC and WoW to name a few).