I assert that book reviews (and music reviews) are irrelevant these days.
I also added to that thinking in a Comment (which I must quote in full since I can't find a way to link directly to it):
See, the thing is, before the Net, you'd read a review in paper. Then you'd have to make a real effort to order the book or buy it at a bookstore or go to the library.
These days, you can quickly sample a book via the Net.
Thus, there's less need for the kind of reviewing that was done in the past. Instead of a "bullhorn" review touting something, a gentle tap on the shoulder to make someone aware of something is all the effort needed today, I think.
Go there and join in the discussion.