This is actually a hard book to review, simply because its usefulness will depend on the reader.
There are solid, research-based strategies presented in a mostly concise format. Formative assessment is extremely important in education. As a teacher, I learn so much about my students in the formative stage that the summative stage becomes a formality, rather than a necessity.
As a veteran teacher, there was nothing much new. However, reading the book was a good refresher, and having all of the strategies in one place is handy.
I think this would be a great read for a beginning teacher--maybe 1-2 years of experience (it would be overwhelming for a first-year teacher who is trying to figure out so much already). It could also be useful in a collaborative group of teachers.