Bottom line up front: Every computational scientist should own a copy of Numerical Recipes but, if you already own a previous version, then don't bother upgrading.
I already owned a copy of "Numerical Recipes in C, 2nd Edition" (from 1992), so I was absolutely thrilled when I saw that the book had been updated in over 15 years. This is why I was so underwhelmed with the 3rd edition. As a previous reviewer noted, the vast majority of the book is largely unchanged.
As in previous editions, the authors do a great job of providing codes that cover the spectrum of topics encountered by researchers. As in previous editions, the authors still take the "give a man a fish" instead of the "teach a man to fish" method. This might seem like a negative but, in my opinion, this is why every scientist should own a copy of Numerical Recipes. Often, topics pop up that need immediate solving and one can often find a code for the topic in Numerical Recipes. As in previous editions, Numerical Recipes is really just an annotated code repository, with very stringent/restrictive licensing rules by the way!
However, as the authors note in the introduction, they made a conscious decision to fill pages with verbatim codes, not building insight into various topics. In my experience, the codes given in Numerical Recipes get the job done, but these tend to be simple and less efficient than other well-known algorithms.
As in previous editions, Numerical Recipes is a terrible pedagogical text. If you're interesting in understanding a particular topic, then get a special-purpose book.