Nielsen and Chuang's book can still be considered the main reference book on quantum information and computation, even after more than 10 years of the original release. I'd highly recommend it to anyone who is looking for a reference to start from.
However, if you already own the original version of the book, be warned that this book is basically a reprint of the first edition. It's true that it comes with a new introduction and afterword from the authors - but the new material is only 4 (four) pages long, and can be found online for free in this very site under the "Look inside" link. This is the reason why I gave 4 stars instead of 5 - I believe that a "10th Anniversary Edition" deserved a little bit more than 4 pages of new information, especially in the case of a book on a very dynamic field.