It's not a review, it's a guide. There's one paragraph mentioning the documentation is difficult and it's well known that like UNIX manuals the NR is reference not tutorial. Besides he says this:
"In spite of these difficulties, LilyPond is astoundingly powerful, and
produces very beautiful output "
It's well know that lilypond is hard for beginners and has a steep learning curve. This is fair comment. The same applies to most powerful software applications. I don't see this short paragraph in the negative light that you appear to, and besides, he goes on to give a quick guide to lilypond, which is useful for people.