"You shouldn't have agreed to review a book in a genre you don't like, it's unprofessional."
Is it not the job of the author to research the best reviewers for their own book? To find a reviewer whose interests and passions are mirrored by their own? To read other reviews by that individual to make sure the traits that reviewer considers important are found in their own work, and the personal gripes avoided?
Unless your book is truly universal, aimed at everyone from a twenty something lad to a retirement aged woman, it's unlikely everyone will agree on the merits of your work. If you romance novel with a strong female lead finds its way onto a closet misogynist reviewer's desk you're unlikely to get the score you were hoping for. Of course you can't stop him from reading and reviewing it, but it would be pretty foolish to gift-wrap it and deliver it to his door personally!
It's important to try to get a good number of reviews, but the majority of those are likely to come from everyday punters, preferably recommended by friends or on forums related to the subject or genre you're writing on. Your 'professional' reviews however need a little more care and attention, matching your book to the correct reviewer to give it the best possible chance is a key part of the process.
Also, I've said it before and at the risk of repeating myself ad nauseum, a lot of 5* reviews aren't worth the virtual paper they're written on and are discounted by potential purchasers of your book. This is especially true of those written by local book review organisations whose sole purpose appears to be to champion local authors. Take every positive review with a pinch of salt, especially if it is at odds with what your some of your customers are saying.
I prefer to point out what I perceive to be flaws, rather than gush about the positives in a book, because fawning over something rarely has an impact. If I give a book a high score, between seven and nine out of ten, it means it's a good book and well worth reading, even if I spend as much time discussing what I didn't like about it as the things I did. We all know what makes a good story, there's no point going on about how the characters were “realistic, well-rounded” and the sub-plot “cleverly intertwined and really added something”.
In future I'm going to have to be more brutal in terms of what I accept for review, I suspect I'll be rejecting over two thirds in the first few pages, with another fair few by the end of chapter three. Much like an agent or publisher I need to be sure I'm going to enjoy the book from an early point, the basic premise has been set up, the writing is of a sufficient quality and I'm being persuaded to turn the pages. So if you're looking for a review for your book, I'd really recommend reading some of my reviews, particularly in your genre (use the tag cloud in the right sidebar), even 'Look Inside' and read the sample of a book I gave high marks, to decide if yours is equally well written.
Don't be put off though, I do enjoy reading and critiquing, even though it takes up a little more of my time than I intended. I've made some great new friends from reviewing, who I can sound ideas off and discuss the finer points of editing and publishing with, so there could be long-term benefit to submitting your book for review.