Core77 is one of the most ambitious online magazines about design. I try to visit now and then even though it is not often enough. If you have not found it yet, they have a nice book review section. Of course, not all books are necessarily interesting, but they are all related to aspects of design. Some of the books I have also reviewed on my blog. I have not really read any reviews carefully to be able to say anything about the quality of them. Maybe I will later.
Take a look.