Instruct: Classify a review into positive or negative sentiment.
Query: A good but unreasonably sized book on semigroups

This book is ok for those who want to study semigroups from a general point of view, as a branch of modern applied mathematics. However, with 574 pages of text, it has the disadvantage of being too much oversized. Also, for those who are interested in specific applications of semigroups, like partial differential equations (parabolic PDEs, stability, properties of solutions etc) this book might appear too vague. So, if you are going to create something new in those areas, your tool will be certainly Pazy's Semigroups, which is shorter, more comprehensive and more applications oriented, without compromising the theory part of the subject. Note that to read these books you need a good background in complex functions, functional analysis and spectral theory in Banach and Hilbert spaces (for the spectral theory I recommend A. Taylor's Introduction to Functional Analysis book, chapters 5,6).