Personal ones. If I had to distill it here, I require that my prose be varied but sensible (e.g. breaks the rules for readability, never egregiously), with no formula, no waffle words, and no meaningless sentences. Tropes can be fine but only used sparingly, naturally, and absolutely not always in the same place. Reading level should be collegiate, but not doctoral, and industry terms should be defined on first use. These are stylistic questions shaped by years of reading professional authors and no AI has any idea how to do that out of the box. Reading what most people put out with AI, I can see the patterns like repeating textures, and it grates on my optic nerves.

I'm making progress on that with mine, but it's a tough problem. Needs manual tweaking even after multiple rounds of automated revision.