Review rich snippets are a powerful local markup type but they have been open to abuse and misuse. Google with release of their critic review snippet extension has also significantly updated their rules for Local Business‘s use of review rich snippets on their website.
IN typical Google fashion, the new rules while adding additional use cases manage to direcgtly contradict the previous rules particularly in regards to whether you can mark up reviews from third party sites (previously you could but you can no more.
At the GetFiveStars blog, I have detailed the new rule changes and which of the new rules you should be aware of when implementing rich snippet mark up on your site.
Head over there and let me know what you think of the new rules.Updated Google Schema Review Guidelines for Local Businesses by Mike Blumenthal