Because many bloggers have a policy of only writing about books they like, I feel they aren't actually reviewing books at their sites, but recommending them. Absolutely nothing wrong with that. In fact Laura Miller has a piece up at Salon called The Fine Art of Recommending Books.
Miller quotes Lorin Stein of The Paris Review as saying, "I don't think people read 'for' pleasure...mainly we do it out of need."
Super librarian Nancy Pearl describes four "doorways" into fiction and narrative nonfiction: story, characters, setting and language. "The difference between books is often a difference in the size of those doorways," she says.