One would be wrong. This book goes into rather impressive depth on some rather abstract concepts of computer science without dabbling for too long in the details. It does the best job I've ever seen of explaining the Turing machine and how it relates to computability and decidablity.
The exercises are both easy and insanely difficult - so you can basically chose your level and then go through the book, some of the problems are very hard, some are trivially easy, a great mix makes for great homework assignments.
The "Proof Idea:" sections before every proof give you the underlying concepts in plain english that are about to be stated formally so you have a clue what's happening when the formal definitions start flying. These are priceless and should be included in every other book that uses formal proof techniques.
The book reads fairly well on its own, or makes for a great class text book, which I used it for. As my professor said, "This is a good book because it doesn't have any extra words." but you don't seem to mind as you read it. Probably the best work on the science of computation in the world, certainly the best I've ever seen.
I always felt that being a cs-tist was about programming, object oriented design/analysis, design patterns, UML, etc.. And there is no doubt that mastery of these technologies are required of any good cs-tist. However, if you want to understand where all these technologies you use come from, how they connect, and to get a glimpse of where its all going, you must combine your current programming and trend following expertise with knowledge of the underlying theories of computation.
This book should be required reading for all first year CS students so that they may get the 'big picture' right from the start and be able to see CS as a whole rather than a bunch of 'kinda related' courses. I see this book inspiring a whole generation of cs-tists - many of whom may have gone into other professions after reading books like 'Introduction to Automata Theory, Languages, and Computation' by Ullman, Hopcroft (a great, rigorous treatment of cs, but *not* a good book to learn from or be inspired by).
Again, great book!
The text IS as good as the best reviews make it out to be (ignore the single 1-star rating). Unfortunately, I do not have the book with me now, otherwise my praise would have taken up the whole 1000 word maximum of the review.
If this is your assigned course textbook, you're lucky. If this is NOT your assigned textbook, USE it as your guide. It makes topics simpler and more intuitive. The way Sipser ropes down exotic theorems into straightforward, understandable logic is almost magical. The book scores in most areas: smoothness of flow, ease of understanding, order of presentation, motivational cues, and thoroughness in the areas covered.
The problem with the book is in the number of topics covered, and in the number of examples. There are not sufficient examples in some cases, and not sufficient material in some cases. This is a small textbook. At the end of each chapter, Sipser often glosses over the more advanced issues. If doing a thorough study, one will frequently need a more complete reference.
This will, of course, not be a problem if your course does not go beyond what is covered here: Finite Automata, Turing Machines, the relationship between the classes of languages, reducibility, and complexity theory.