I looked at your plugin as I was in the process of creating a review website. Well done with keeping it simple.
1. In ratings CSS images are loaded from absolute URL's make it relative to avoid conflict. Change rating image url to ('../img/star.0.png')
2. Using general function names. It's not good practice to use names such as extendcomment etc.. using something more unique. This will ensure you don't have clash with other plugins.
3. Check your schema.org settings. It's not according to spec. See here http://microformats.org/wiki/hreview-aggregate. Tool used to check . Microformats chrome extension.