I think I understand you, Grac, and you're right. "I want more H/C" is an opinion rather than a literary criticism (in the sense of "your characterization here puzzles me" for instance) -- but on the lists, often taste (or flavor, to use your term *g*) is what's being discussed, and it's where the unpleasantness comes in. It's a reasonable distinction but one that generally blurs on the lists when discussing a fic. It's an easy line to blur unless someone comes in and dissects the reader's reactions to learn whether she hated the story because it was H/C (e.g.) or because it was poorly done H/C.
But I would say my point covers both "taste" reviews and structural reviews. There's nothing wrong with saying, for instance, "I prefer even bad chocolate to good strawberry," though it's a "taste" and not a literary criticism. But you don't have to say "These strawberries suck!" :)