I've been remiss in writing reviews, but I have to admit that nothing makes me happier than when an author replies directly to my comment. Notable for this are H Dean and lovelyandsad.
Sometimes I click on a story and realize within the first paragraph that the writing doesn't appeal to me at all. There are a LOT of stories on the site, so if the opening is full of typos and stilted writing, I don't have time to finish it, and I feel it would be rude to pass judgement because I didn't consume the whole thing. I also won't comment if an author has been argumentative with a reviewer. That said, I will try and comment more frequently, it's just not always as simple as "Good story 10/10."