I have been having an entertaining time reading about review scores for games lately and comparing them to what actually came out the other end. Tobold recently complained that previews are pretty much useless as they are just marketing from the game companies and that there are far more of them then there are reviews. It is definitely true that the hype surrounding a game is an important predictor of sales but that promises contained in previews are pretty near worthless in terms of figuring out whether or not a game is worth buying. I am reminded of the Bears, Bears, Bears speech promoting Warhammer Online that people got so excited about but which turned out to be complete rubbish (though I called it out as such at the time, go me!)
Certainly Tobold is right that previews are worthless in terms of promises, though you can likely glean some information from watching actual gameplay footage. You just have to completely ignore anything anyone says and only look at what you see when someone is doing things in the game itself and you just can't get much out of that. Sadly I don't think that reviews after the game is out are actually much better. Unfortunately there is way too much of people who played a game for 100 hours in the first two weeks complaining that the game is the worst thing they have ever played and not worth the $50 they paid for it. These are the same sorts of people who sit on forums for a game they have logged thousands of hours in and whine endlessly about how the game is garbage.
The real problem here is expectations. When an indie game comes out with no expectations and little fanfare people who don't like it stop playing but they rarely go ballistic and post 1 star reviews. Just another mediocre game, right? But when it is a much anticipated big title things are very different and people invest huge amounts of their persona in being fans of that particular game. Any disappointment in how the game turns out becomes a very personal attack against them and their judgement and they lash out. It is much like interpersonal interactions in that if a stranger utters some nasty slur it is going to irritate me but it isn't going to wreck my day. A friend who I have spent months telling my friends is a super sort of person who does the same thing is going to be a much bigger deal and my reaction will be much more vitriolic.
The only way to get useful reviews about a game is to only accept information from people who you trust to have similar tastes and judgement to your own. Any sort of large scale system is going to be completely corrupted by marketing, whining from bittervets, and false hope. Even if game quality were some sort of objectively measureable quality (Hint: It isn't) then actually finding that information would still be a mess. It seems like with the giant information collection device that the internet is that we could actually figure this stuff out but the systems that are in place right now are pretty lame at doing so.