When reviewing we don't often get drawing files and it is normally printed plans or pdfs.
The scale. If the scale is too large to read anything on the plan then it is useless.
I was sent a drawing the other day that was a single A2 sheet of paper (which is an unusual sheet size for what this was of) and had a scale of 1:5000 or something ridiculous like that and they'd obviously done all their annotation in modelspace (no annotative scaling) so then in their 'final' plan the text was about half a mm high and totally unreadable. The drawing should have been split over several sheets at smaller scales so that is is actually readable although their drafting department is either really crap or just plain dodgy trying to cut corners and time. We sent it back to them.
Another thing that annoys me is when someone does something really well, then in other aspects of the design it is substantially lacking. Yes, it is great that you done component A really detailed and the design does look good. So why the heck didn't you list any design data at all (no levels, grades, sizes, anything etc) for component B which is just as important on your construction documents?
If you specify that X is required to be satisfied in your design then clearly show elsewhere on the plans that X is not satisfied, well... (which only came across my desk after it was already approved and had been constructed and no one had picked up on it yet).
I like plans that have good legends, scales and follows common industry practices somewhat.
Don't use comic sans as a font.