I really don't like the idea of having an arbitrary system of judgment when it comes to rating: ratings affect contributors' general ratings as well as how customers weight the review. Those things are fairly serious. I don't take rating reviews lightly because I know time goes into their making and purchases are based on them (and their reception).
I personally am a little turned off by the idea of something "not feeling right" and it being voted down as a result. If you are not conscious of the reason why, you may be voting based on something very biased. To me it's not fair or professional to give a "useful" rating to a review that includes everything, has no apparent flaws, but didn't make you "feel" some ambiguous thing. That also makes it difficult for reviewers such as myself to improve: if we don't have a critique, we can't become better.
I also think that syntax/rules of written English/blabla are important; if you can't understand the review then you can't take anything away from it. However, it's important to keep the intended function of grammar in mind. The function of grammar is not to give a false sense of superiority to people that have the privilege of education/the kind of mind that is able to "perfectly" apprehend all of its devices. The function of grammar is to provide a standard that organizes written and spoken language so that we aren't all speaking or own little languages. In other words, so we can understand one another. So I don't really care if someone misspells a few words so long as the interview is coherent and the mistakes aren't distracting.
All that said, I more or less adhere to Carrie Ann's guidelines with a slight alteration. I ask a lot of questions, so my criteria is more like "Am I left with questions about major issues like material, cleaning, functions, use, etc?" I can come up with a question for pretty much everything.