The Michigan Law Review has put out a call for contributions to its annual book review issue. That solicitation, which I saw at Concurring Opinions, includes an assertion that strikes me as enormously silly: Please note that we require that finished drafts be no more than 8,500 words, including footnotes. We believe that this is the ideal length for an interesting and useful book review."
In my life, I've read some fabulous 200-word book reviews and some horrible 200-word reviews; and I've read some fabulous 20,000-word book reviews (really, review essays) and some horrible 20,000 word reviews. The idea that there is an "ideal" length for every review of every book is just so... so... so ... crazy!
That's not to say that the editors of the book review issue of the Michigan Law Review don't have good and sound reasons to restrict page lengths, including to save space for a greater number of reviews in each issue. I'd even be willing to stipulate that, on average, 8,500-word reviews are likely to be better than 12,000-word or 20,000-word reviews. But the idea that there is some "ideal" or "optimal" level that applies to all reviews is just enormously silly.