I usually only use a review to 'confirm' a feeling I've had myself from watching gameplay videos and the like. If a review is in line with my previous thoughts I do what I plan to do with the game. If it's not, I'll go back to the videos and make up my mind from there.
I will only read reviews of games I'm not sure about anyway, no review will sway me if I already made up my mind one way or another.