There are large portions of the book that are used to prop up the central claims about the role of representation in scientific discovery that are probably not really necessary; the extended discussion of Maxwell could likely be a lot shorter, but given that the book itself is pretty short and to-the-point, that complaint is a pretty trivial one. All-in-all, this is a very good piece of philosophy.
I'm already sympathetic to most of the views advanced in the book, especially regarding mental representation. I suppose the major concern that I have is that the actual discussion of representation really is the major substance of the book, but it is not the way that the book is sold. Nersessian titled the book (and pitches it in the opening section) as a book about the creation of concepts, and it really isn't. It is really about a way that scientists do conceptual analysis to further their research. That's an interesting project, and one that is engaging and exciting, but not really the same thing.
I do strongly recommend the book to those interested in that sort of thing, though, and the book is accessible and well-written, and should be a relatively quick read for anyone who is conversant in the background psychological literature that Nersessian is working with. The case studies with Maxwell and the unnamed engineer-type-person are informative, and tie in well with a lot of literature (which Nersessian discusses at length in chapters four on until the end) in cognitive science.