This will keep me reading for years, and it's surprisingly well written.  The problem with a book like this is that it can't really afford to go into depth (or it would grow to titanic size), but I guess that it's purpose is to expose people to interesting mathematics where they can get enough of a taste to know when to dive deeper.  It does require discipline to stay on track at times, but it's worth pushing through (although I'm not finished yet).