I don't remember if this topic has been talked about recently, but here goes...
I've read when sending out ARC to beta readers it tends to be more effective when you provide them with a list of questions. What do you ask?
These are the ones I've been thinking of.
Did the book feel too long, too short or just right? (Addressing pacing)
What did you like about the Main Character? What did you dislike? (Characterization)
What was your favorite part of the story? What was your least? (This can address many things but I would hope for plot holes or slow sections of the book)
Did you notice any big oopsies… wrong eye or hair color, wrong place wrong time, any over used words or phrases, etc.
How did you feel when you finished reading the book? (Overall storyline)
At any point did you want to put the book down? If so where? (Soggy Middles)