I think my style for critiques is to-the-point and supportive, because that seems to be what I respond to best when being critiqued myself.
I once had two different people read a draft of some chapters, and they both noted the same sentence (which was good, yay for knowing where to edit!), but one of them said, “I would stop reading RIGHT here; I hate this character” while the other said “are you sure this is how she would respond? seems out of character.” The second was so much more helpful!
I strive to critique in the second style: first attempt to get a good grasp on characters, see where their actions seem off, then look at how they interact with what’s going on around them.
For me, at least, a lot of my plot problems are caused by my characters acting out of character and then my altering my plot to go along with it.