- poor structure. Bad setup/payoffs, useless sequences, confusing narrative without any merit behind it

- poor pacing. Too much "brain-off" action, shitty dialog, too fast/slow for the theme

- uninteresting characters, with no redeeming characteristics (e.g. a great actor or enough plot quality to compensate)

These in decreasing order of importance for them -

They will certainly critize other things (plain scenes, bad framing, technical flaws, bad lighting, etc.) but I don't think I've ever seen them give a purely negative review based only on these.

If any of those three criteria above are met, though, (and god forbid all three) they will absolutely pile on a terrible rating with complaints on how the scenes are ugly and general filmmaking is lazy.

Oh, and also, they'll point out most editing errors, seeing as they are editors too.

And insert pointless Star Trek references no matter what, of course