Charlie Anders (author of Choir Boy) addresses this question--responding to the flap about Michiko Kakutani in Slate--in her blog (unfortunately, she's doing the barebones blog thing so there's no permalink. Just go here and find "[2006/04/12 8:08 pm]")
I definitely lean towards the friendly/balanced school of criticism. Having read one or two reviews of Choir Boy that made me feel pretty demoralized, I don't really want to inflict that on any other writers. At the same time, I'm pretty clear that my mission as a book reviewer is just to let people know whether a book is worth buying and reading.
(A side note: I've always thought that there's no point in writing a negative review of an obscure or independent book. Most people won't even have heard of it, so screaming "don't buy this book you've never heard of!" seems kind of pointless and mean.)
Actually, the first question any book review should answer isn't, "will I like this book?" but rather, "why should I even care about this book? What's interesting about it?" ... And then you do have to address the "does it suck?" question. I have to admit, I go about this somewhat obliquely. Partly because I try to see the good in everything, and partly because I'm still a peon and don't want to overstep my authority. ... It's true that different people have different tastes, and you might love a book that I kind of hated.
I'm not going to state here that Charlie's wrong. I think different reviewers need to have different missions, and that, to keep the book-buying business alive and well, we need reviewers who quite simply tell a book-buying audience whether or not to buy a book. I also agree wholeheartedly that most reviewers need to be boosters for books -- giving people a reason to buy books, rather than a reason to spend that money on a movie instead.
However, I do think that all reviewers need to at least be aware of the "higher" purpose of serving and furthering an art form. (Let's pause here for you to cringe.)
It's easier now than it ever was to get a novel or a memoir published, and easier now than ever to get it read. Yes, despite the moaning and groaning, if you look at the numbers the right way, you'll see that more books are actually being bought than ever before. (Unfortunately, I'm too lazy right now to look up the stats and do the math. Will do some other time maybe.) What this means is not that we have more people working together to study, enhance and further the art form/s, but rather that we have more pressure on barely competent writers to produce, produce, produce. The stick is short deadlines for drafts. The carrot is three-book deals on the one hand, and warm reception on the other.
Literature is indeed walking forward; memoir and fiction have and continue to meld and affect one another. However, given the sheer amount of memoirish fiction and fictional memoir that has been produced in the past decade, it's shocking, appalling and lots of other prudish, literary -ings, that the last even minor literary "breakthrough" on this front was A Heartbreaking Work of Staggering Genius six or seven years ago. Since then, there have been a lot of imitators, and even more people who neither imitated nor innovated, but simply took Heartbreaking Work's success as an excuse to walk backward to a satiate, safe, and unchallenging prose style telling stories that they know will be well received because they have been told so often before.
Readers--perfectly intelligent, literate and well-educated readers--will naturally, in an initial phase of learning to read books, be hostile to the things they read that are unexpected, unusual (to them) and challenging. Anyone who has taught literature or taught writing by having students read literature will be aware that hostility to the new and challenging is not just typical, but almost necessary. The key is to not let your students get away with it. They can hate a book, but they also have to read it through and analyze it intelligently. And I guarantee you that the book they hated, the book they so competently and passionately analyzed to pieces on their final exam, is the one that will stay with them, that will affect they way they think about life, and will inform their ideas about sophistication and competence in literature in the years to come.
But in the process of taking book production from a manufacturing industry to a service industry (like Wal-mart or McDonald's) the book industry has turned from offering art and forcing those who want art to take what they're offered, to mass-producing entertainment, and enticing people to buy it by packaging it as art. Both publishers and critics are now letting readers get away with their hostility towards the new and the challenging. They are encouraging readers to ensconce the idea of literary art in a fixed set of plots (self-discovery, familial healing), fixed settings (urban or suburban, middle or upper middle class, white, professional circles), and fixed prose style ("poetic", with an emphasis on descriptions based on lists and visual metaphors) and techniques (indistinguishable first or close-third person, with voice indistinguishable from author's voice; obsessively shaped sentence structure and rhythm, emphasis on the turned phrase; beauty of authorial voice takes precedence over the needs of the story, etc.)
With these points being the hallmarks of "good writing", anything that doesn't follow suit is necessarily considered "bad writing", and anything that touches on these points is necessarily considered "good writing", whether it actually is or not. (And I would contend that anything that touches on these now cliched points is almost guaranteed to not be good, because you have to be a genius to write well through cliches.) Readers don't have to question, just passively receive. Anything that challenges this order is thrown across the room (if you're me) or quietly dismissed with a "I just don't like to read that kind of thing."
You never have to leave the zone of books that tell you the same comforting things over and over again.
The only thing that can possibly counteract the walmartization of book production is competent, purposeful criticism. If that. Because if the reading public, the self-selected, self-described literary top-percentiles are accepting the description of good literature I've outlined above (and they are), then it is because the critics who truly shape opinion are either permitting this, or actively promoting it. I rather think it's the former: that critics permit this because they're stuck in a book-by-book critical mode, seeking to place the book in its own context, but not in the context of literature in the early 21st century, not in the context of literature against the background of its own traditions, or of the future annihilation it faces as new entertainment media become increasingly culturally sophisticated--become, in short, art forms.
As literature becomes increasingly personal, it becomes increasingly self-absorbed and cut off from the implication of interaction with society in general. New digital media can stand this transformation and continue to turn it on its head--I don't think printed literature can. As it grows more personal, literature ceases to challenge and produce new ideas. As it ceases to challenge and renew, so it dies. And for those of us who love words on a page, this is simply unacceptable.
I want to see critics who write every review in full knowledge of these trends, in full consciousness of the tradition both they and their subjects are writing in, in full awareness of their role in supporting an ancient art form. I want critics to use every book as a positive or negative example of how the art is being developed (or not) and where it is (or isn't) going. I want critics to give every book its due respect, by respectfully reaming those books with no ambition, no art, no challenge. I want even a book that passes that basic test (does it challenge, or seek to present something new, or seek to develop an aspect of the art form in an interesting way?) to be thoroughly analyzed for how it does it. I want reviews to teach me more about the art of writing than I already know myself (because how sad is it when a review is less knowledgeable about writing than I am?) I want to be able to read reviews of books to get an overview of the state of the art--no, in fact more than that: I want to read reviews for their own sake, because reading books, and thinking about books, and having my own perspective on books won't be enough for me. I want someone brilliant and supremely knowledgeable to enhance my enjoyment of books with a view that I could never have. I want reviews that are reading material in themselves, and not just conduits to reading material.
Is that too much to ask?