One other thing to bear in mind about professional critics is that they have to cover everything, regardless of whether it appeals or not, and write about it objectively.
This is not universally true. Professional critics don't always have to see everything (and it isn't necessarily desirable to do so). A critic should see enough to know what he's talking about, but seeing too much can dull the senses of reviewers who really have to see everything, such as movie critics for popular publications. I see what you mean about "objectively" - no critic can be truly objective but bloggers are at liberty to be fans, whereas critics should restrain such feelings insofar as humanly possible.