Functions of complex variables, Mathematical analysis
For me this text is a joy and a delight. In the preface the authors remark that to acquire a thorough grasp of the subject requires hard work They assert the virtues of this book to be clarity of presentation, selection of topics, and interesting exercises. They express their hope that the book will help the student to become as enthusiastic about the subject as the authors are. In my case they achieve their goals.
Very many years ago I took complex analysis in grad school using the then-recent text by Ahlfors, and with a 100% Teutonic professor; I then found the subject boring. This book, however makes me enthusiastic. It is one of the few math texts I own that I like for bedtime reading, opening it to something of interest, or just to a random section or some exercises, and relaxing while reading as if it were an adventure novel. When I put it down, consequences trickle through my mind as I go to sleep. No, it's not an easy subject, but the authors make it an enthralling one, at least for me.