I tend to read the VGchartz reviews and nintendolife's reviews (nintendolife reviews every VC and WiiWare release in a couple of days and I agree with most of their reviews).
I find metacritic (and other such sites) to be worthless.
However, I have found that nothing beats the user reviews of amazon. Look at the average of the user reviews (which amazon automatically does), and you will instantly know if the game is good or not.