I'm another author who has no problem with critical comments about my stories. They are not my *favorite* comments, of course
but I still like them, because (1) they are tangible evidence that someone has actually read my wonderful creation (the only kind I get, really), and (2) sometimes they can lead to an interesting dialogue about what works in stories and what doesn't.
Positive comments are more fun, of course. I agree with Malcatraz, it is best when a comment reveals that the story was understood. A good strategy for writing comments is to say things like "I especially liked the part where ...".
As a commenter, I probably comment on about 1 in 6 stories I read, which is a much higher ratio than I used to. On the other hand, I have much less time and/or inclination to read these days, so I probably comment less overall. It's one of those things, as Fi says.