As someone who used to work as a proofreader, and who does a lot of proofreading still, I can't help but notice when commas are misplaced, or there are spelling errors. So I tend to point out those things when I'm going through the MS.
At the same time, I leave comments where I think things are unclear, out of character or not in keeping with the rest of the story. I ask questions when things don't add up and point out inconsistencies in description, timeline or sequence of events.
Only when I get to the end do I do an overview of what I've thought of the book, its strengths and weaknesses. I like to offer suggestions of what could be done to fix any problems I've identified.
Some books have bigger problems than others (my own has some pretty major flaws that were pointed out by my beta readers), and some can be more easily solved than others. But my question is, how much detail do you want when someone is reading for you? Do you really want to know the last third of the novel really doesn't work?
Personally, I want to know as much as possible. If the last third doesn't work at all, I want to hear it. Without this kind of feedback, how do I know what needs fixing? So I tend to go into every beta read wanting to give the same kind of critique I want to get back.
But I get the impression maybe other writers aren't prepared for that level, that maybe my notes are too harsh, or too extensive. I don't want to hurt anyones' feelings, but I don't feel that I'm doing anyone a favor if I don't point out what I perceive as being problems. Just saying 'this is awesome' means nothing if it isn't followed up by reasons why it's awesome. Or reasons why it isn't.
Does anyone have any thoughts or opinions on this matter? How detailed are your notes when you beta read?