I guess that makes sense for a small crag, where one can easily look over most of the rock before starting out.
There are so many guidebooks out there, I wonder if any have a 'reviewer system' like that I described. I have a very interesting guidebook for Elbesandstein in the former East Germany. It doesn't include route reviews as far as I can tell, and does not have any stars, but it has various accounts, old handwritten letters, and copies of newspaper clippings. These are mostly to give a historical perspective on the area, but they also give the reader a feeling about some of the routes, which is a little bit like a review. The photographs serve a similar purpose.
I like reading reviews of movies and books, as long as the writer is good. It helps to have several reviews to consult, as there are usually several viewpoints. So, if I ever write a guidebook, I might try such a system and see how it goes (probably badly, as most of my efforts go...)
Jon