Danny Ayers has written up an RDF-based Review Vocabulary. I think it would work well as an interchange format for reviews, but perhaps not so well in an RSS feed.
For example, the dc:creator field seems to apply to the reviewer rather than the item. The description is blank, because it can't contain the review:text field, and the title of the post has to be the title of the item under review. I think the description of the item being reviewed (URI, title, artist, etc) should be in a block separate from the RSS data.
I like review:reviewer, embedded within the review section rather than outside. However, I still stick with my decision to use a user-defined rating scale so that not everyone has to use a 1-10 scale (as most people don't). And I think it needs more description of the type of object under review (I had to manually search Google to find out if it was an album or a single track).
Maybe I've just thought about this too much (or not enough).