Pros: Entertaining; nothing inaccurate or misleading to be found here; handsomely printed book.
Cons: Mostly fluff; glosses over interesting details and much of the actual science.
The Universe in a Nutshell is a handsome, if busy, book (if only all science books received this treatment from publishers!) and it is written in a clear, engaging style, but the content itself is mediocre.
Popular science, especially popularized physics, as a genre has a tendency to emphasize the "gee whiz" factor instead of bringing the reader to an understanding of the topic covered. Hawking's previous popular work, the masterpiece A Brief History of Time was a splendid exception to that rule. The Universe In A Nutshell is not.
I am a working physicist (albeit working far from the field of cosmology) and must say I gained little from reading this book. It is possible to answer the questions "Why do we believe X to be true?" and "What precisely do we mean by that?"--to communicate a physical intuition or mathematically-formulated truth--to an audience capable of mathematical and physical reasoning but not necessarily familiar with the specific techniques of a discipline. A Brief History of Time stands as testament to that. The Universe in a Nutshell, however, glosses over most of the physics to focus on phenomenology and description of the consequences of current theories, which the reader is left to take on faith.
The section on string theory and "brane" theory is almost an exception to this, however, so much is omitted that the reader is left without an understanding of what a string/brane is or why some working in quantum field theory think they might be used to formulate a unified physical theory.
If you're looking for an entertaining but cursory overview of some currents in cosmology and QFT, or perhaps a gift for a very young teenager, this book is recommendable. Otherwise, books like Hawking's Brief History of Time or even less objective books like David Deutsch's The Fabric of Reality make for more satisfying reading.