I think book reviews are great and they do help to sell books or at least make people aware that they exist. Any exposure a book receives, especially a book review, is great for any author. I have three 5 star reviews posted on amazon.com. I try to get all the book reviews I can when the opportunity presents itself.
Yes, book reviews are essential. People want to know that others have read the book and that it was worth while... otherwise they have to rely on the publisher's copy in making their decision, which everyone knows is not objective.
You could say I am biased, as I write reviews for a weekly Turkish newspaper. But let me give you an example: as part of my remuneration I receive an advert for my bookstore on the same page as the book review. Regularly we receive emails from readers wanting to buy the book reviewed that week.
Check out my style by seeing today's article: a review of Marco Polo's The Travels, which I compare with a Lonely Planet guide.
The review as ALWAYS in the top 10 read articles on the web version of the Sunday newspaper, and is regularly top 5 or even top 3.
If you would like me to provide a review for your book, send me a message!