The customer reviews can help a lot to choose a game. Does someone know how the overall score is calculated? I've got the impression that only an actual review counts towards the end score but if a review was helpful it doesn't have any additional weight.
The Steam FAQ only says this:
Q. Do these written reviews create an overall score or rating for a product?
A. Not yet, but we are looking to add that during the beta. Many products on Steam change significantly over time as the game or software is updated and new content is added. In order to form a score that accurately reflects the current state of a product, we first need to gather and evaluate the data from reviews.
This FAQ entry seems also to be a bit out of date. Because games do have an overall score now. Oh, by the way. Games with an "Overwhelmingly Positive", so with a score of 95% or higher, should have a golden thumb in the search results, not a blue one. Just for glory!
... and games with a red thumb should not appear at all!