I'll go on my impression of a demo more than review score. If there's a game I'm really interested in the review score won't relly affect my decision to buy. If there's a game I don't really care for then high review scores won't affect my decision to not buy. If there's a game I think I may like but I'm not sure then review scores will probably sway my decision if there's nothing else upon which to make a decision.
examples:
Bayonetta, the demo didn't really impress me, so the review scores aren't going to convince me to buy (post patch Bayonetta should be sufficiently comparable to 360 as makes no difference).
Dante's Inferno, I liked the demo, and if it wasn't for the impending God of War III it would be on my get soon list, as it is it's on my get eventually list. Review scores didn't influence me.
Darksiders seemed like a maybe but wasn't really on my radar, the reviews coming in for it has probably put it ahead of Dante's Inferno on my list of H'n'S games to get. I may end up getting it before GoW III comes out if the price drops a wee bit more.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix