This is basically my answer as well. I'm the first to admit that my tastes are not very well in line with conventional wisdom (I also cant stand Pixar films..) The closer your tastes are to that sort of normative, middle of the road taste the more useful aggregated reviews will likely be.

Using a single reviewer (or several) only works when someone's tastes are predictable. Using aggregate reviews, can remove the kind of predictability that I can use to predict wether I'd like the movie.