How much do you research a game before you buy it?

Like others here, it depends.

If its a series I love (Halo, NCAA Football, Forza, Gran Turismo, Final Fantasy, GTA etc..) I tend to buy it on day one. Also, certain developers (Bungie, Bioware, Blizzard etc..) I'll buy games without much research as I tend to enjoy the games they put out.

Other than that, I usually read a variety of reviews and impressions to make a decision. I don't just look at scores but the actual content to determine if I would enjoy the game.

Normally if it is a game I have not been following I go to gamerankings and use it as a hub to check reviews. I tend to check IGN and Gametrailers first since they are the first ones with video reviews. I read 1up and GS ocassionally too.

Prices are something I tend to check instore as walking around a few stores and checking prices (1st and 2nd hand) tends to give you a good feel for what is or isn't a good price.

I often check the really negative user reviews on games as well as these reviews tend to highlight the smallest most nitpicky complaints that can be aimed at a game.