:But he never says exactly what it is that irks him!

May I put forth two ideas?  First of all, he is not going
to write your fanfic for you.  If he says "Akane way too
sluttish in this fanfic!" he's not going to tell you exactly
where and how.  That's not his job, it's YOUR job to weigh
his criticism, pick the spots, and fix things up.

Secondly, he is only one commentator of hopefully many.
If his criticism seems to be useless...don't use it!
Based on what you are saying, people who drop you a line
saying "great fic!" and nothing more are also a waste
of your time.  I don't think that's true.

signed, pnt