What do I look for in a book review?
I look to see if the reviewer has actually read the book or just copied the book jacket blurb.
I look to see if the reviewer had any emotional investment in the book, if they give a sense of whether they enjoyed the book or not - not merely the words telling me they did or didn't.
I look to see if they are just reciting what they read, or if they are trying to entice the reader into reading the book, or conversely, warning the reader away for specific reasons.
When I write a review on Amazon, I try to personalize it, to make it into a conversation as if I was telling a friend about the book or whatever I am reviewing. Unless the synopsis of the book has already been mentioned numerous times, I'll give a brief summary of the key points. I try to avoid spoilers as much as possible. I try to convey my gut response to the book - if I enjoyed it, if I disliked it, if I learned something from it, etc. I also try to give the reasons for my reaction so people can perceive any bias on my part that I might not even be aware of.
Examples:
A scissor review:
http://www.amazon.com/review/R32WUEU...cm_cr_rdp_perm
My review of "Hounded":
http://www.amazon.com/review/R2UGPLD...cm_cr_rdp_perm