There's a lot of evidence that minimizing dimensions--even to the point of getting rid of obviously relevant ones--generally works best. Though Zagat does have food, decor, service, and cost so it can work especially when you're focused on a single thing. It gets harder when you're rating different things that span different dimensions. Amazon, for example, obviously just has a star system and DVD reviews are this sorta annoying mix of reviews of the movie and reviews of the specific DVD product.