Haven't trusted the major review sites in years.
1. Let the game be out for a bit, then
2. Go visit metacritic and pay particular attention to the lower pro scores. Look at the user scores also. Gamespot does have user reviews and there is always gamefaqs.
At gamefaqs poke the PC button and stop to marvel once more that whatever else may be shown on the listing of the top 10 games and boards, Diablo II LoD is always there!
3. Visit the official forums, if any. Head straight for the Technical Support section.
4. Firingsquad is always worth a visit. www.firingsquad.com They do not review everything, but their reviews tend to be in depth. And sometimes a bit contrarian and cantankerous. I mean you, Jakub Wojnarowicz!
This is also a great site for hardware too! If nobody on their forums has heard of your new game, it is usually a bad sign! Usually ... they gave Civilization 3 96%; but they never reviewed Civilization 4 unless I am missing the link.
5. Plug the name of the game into your favorite search engine with extra words like sucks, won't install, crashes, etc. Surprising what you can find.
6. Head on over to youtube and see if there is anything interesting there.
After you have done all this, if the game looks reasonable then conclude that it will be even better with an expansion pack or two and the best deal will be the bundle in 3 to 5 years!