It's a good idea, but the issue arises that ratings are entirely subjective without context and can be misleading.
Let's take Pulp Fiction as an example. It's considered to be a fantastic film. 10 stars all around.
Personally, I hated the movie. I found it boring, crass, and poorly made, but I also get why other people (seemingly everyone else) like it.
If all I saw was a rating system that told me I had to watch the movie, I would wonder just what the hell everyone was smoking, because there's no context.
Don't just tell me that it's good or bad. Tell me WHY it's good or bad. If you can't do that, I have no interest in your opinion on the matter, because you really don't have one.
Getting into the why is why we have threads