When you write, or more specifically when you publish stuff, these people called reviewers turn up and tell you what they think of it. The knowledge and ability of reviewers varies wildly, but in the anything goes blogs e-sites world, most of the reviews are written by people who haven't a clue what they're talking about. Gone are the professional reviewers in newspapers. Now we have Moe, who puts down "It was really bad." Followed by Larry who puts down "It was good." Do either of these provide anything particularly useful? Not really.
I used to get ripped by some guy who I once rejected for a project. He seemed to make it his life mission to bash me at every opportunity--always anonymously. But always with the same telltale poor spelling that gave him away anyway. Alas, I haven't heard from him in a while.
A good review should contain objective information where a potential reader could decide whether to purchase or not purchase a book they might be interested in. "It was bad" is a little lacking in detail for that. The blog type of review sites seem overwhelmed by the number of books out there. The paid professional reviewers seem to have disappeared. No wonder the publishing world is in so much turmoil, eh.