To begin with, there's the New York Times Book Review, the New York Review of Books, best essay writing services uk and the London Review of Books. They get highly-qualified scholars and writers to write their reviews which are often much more than just a review of the book under consideration. You may have to pay a subscription fee for some of them, but hey, you get what you pay for, as you have discovered. And I think some of them offer free access to at least some of their content.