The book is excellent, and whilst the D20 system isn't perhaps the best choice to work with, it does mean that the basics will be instantly familiar to a large amount of experienced roleplayers; this gives the game an above average accessibility.
However, my major gripe is with the rules for the One Power. Using the D20 system is all well and good on the whole, but did they have to base the One Power system on the spell rules? I don't feel having set weaves does anything to reflect the flexibility of the one power, and I would prefer to see a system there which does- perhaps something like the mage system from White Wolf? Obviously, it would take some work on the part of the GM to adapt, but I feel it would result in a better game if the One Power is to be used by the players at all.
The One Power rules are the one flaw in an otherwise solid and satisfying game.