Having spent a fair bit of time recently researching for my upcoming first Triathlon, if I were to be very hard it would be true to say that there is nothing in Joe's book that isn't already available on the web for free, somewhere. Triathlon for beginners stuff does abound, kit suggestions and explanations are plentiful, and there are more training plans than you could shake a pointy stick at out there too... and all for free. If you are also somebody - as previously suggested - that has a background in general fitness maybe the training plans aren't quite for you as they concentrate (fairly enough given the remit of this book) at those that have little to start with. It will really benefit those that don't have any great fitness base to start with (better than couch potato maybe, but certainly not anyone that is already running 5Ks or peel off 1K in the pool on the way home from the office etc).
However, this isn't to suggest that Joe's book is worthless - far from it. It provides a comprehensive one stop shop on where to start, quickly debunks many triathlon myths (e.g. triathlons are all ironman distances or require budgets of 1000s) and is full of motivational snippets that do leave the reader with the feeling that they WILL complete their first triathlon. The nutrition chapter is worth the book alone for beginners, as also previously stated.
If you are considering your first triathlon, aren't already on any endurance based exercise program and need somewhere to start your research you can't go wrong.