Because pockyimp asked me yesterday and I have no entertaining content of my own to contribute, everyone gets a link to El Santo's explanation of why a reviewer would do negative reviews (in this case, referring to webcomics) rather than sticking by the old adage of "Don't like, don't read".
Personally, I appreciate negative reviews (or, ideally, negative aspects of a review which also makes note of the positive) because they're often more helpful than "Your comic's great, keep doing what you're doing!". Don't get me wrong, the latter is good for keeping the creator from feeling like all is for naught, but from the standpoint of improving negative criticism is far more valuable. Sure, the particularly harsh types can evoke a prolonged twitching spell, but it's worth a little discomfort if the content is ultimately useful.
However, the seriousness with which I take the criticism is in direct proportion to the degree of effort the critic puts into delivering it and his eloquence when doing so; "Your comic sucks" with no elaboration isn't going to get much of a reaction from me one way or another. El Santo's reviews, even the negative ones, are not of this sort. I find him quite entertaining and you should give him many hits. (You may find new comics.)
Bonus Characterization Exercise: Write different characters performing the same action (packing for a trip, going about their morning routine, etc) to get yourself more grounded with their behavior. Personality informs behavior. If you're writing one go-getter morning-person and one drag-ass slacker with identical morning routines, you're doing it wrong.