Most are pretty good. If they're references for students doing homework assignments, I think they give just the right amount of information.
Now, ready for the critique?
The only book I have a mild reservation about is Self-defensive spellwork, because it's so short and most of it I could have looked up on the Lexicon. To improve it, I suggest adding site-specific incantations for the spells which have no incantation listed at the Lexicon.
Additionally, many of the spells are cited as having no incantation because they're non-verbal, but when Harry&co were learning non-verbal spell casting they were required to focus on the incantation of the spell (Harry learns Levicorpus by saying the incantation inside his head in HBP), thus this goes against what we know about non-verbal spells.
Now, I realize that this book might have been written in accordance with what the DADA professor is teaching, and I'm contradicting them. In fact, since so many people who posted before me seem to like the book, I probably have. I'd just like to make it clear that this is my personal opinion and that I'm not trying to attack anyone. I know that I can sometimes sound harsh when I critique other people's work so this is a bit of a disclaimer if I'm coming across that way.