In some regards, a reader's review can provide good feedback, but personally I think that most worthwhile feedback you can get from a reader is going to be subjective.
The things that are really useful--plot problems, errors, poor writing, and so on, are the things that can really help an author improve, and those are things that should be picked out by beta readers before the book is published. If the readers are picking up on those things, generally speaking the book was published too early.
That being said, of course there are published books out there with author complaining of just that. I read a very famous fantasy book* that came highly recommended, and I honestly couldn't believe the book had even been published. Sophomoric dialogue, plot holes everywhere, inconsistent characters, and humor that just wasn't funny. However, the vast majority of readers saw none of these problems and I honestly think most of it was subjective--what I saw as a plot hole might have been part of the satire for someone else. Stilted dialogue was stylistic, and so on.
I guess what I'm saying is that, generally speaking, readers might point out problems, but those problems (at the professional level) are usually going to vary based on personal opinion. One person might hate the way your book ended, the next might love it. One might think it too dark, one not dark enough. One might love your MC, and the next hate them. And so on.
Those opinions do you no good as an author. Fighting to please everyone will never work, and how do you know which describe a real, legitimate problem and which are those subjective opinions? Writing to try to please all of them is a good way to drive yourself crazy and it won't improve the writing.
Unless readers are all pointing out a similar flaw or the vast majority share an opinion, I think reviews should be taken with a grain of salt. I honestly believe that good beta readers and editors can help uncover most of the major errors in a book and if most of the readers are pointing out big flaws, the book went out there far too early.
*Not what you probably think it is.