I am in the process of converting from D&D 3.5 to Pathfinder much later than everyone else. In general, Pathfinder is an impressive system and the true inheritor of the Dungeon's and Dragon's brand. The problem with 3.5 that it emphasizes combat too much and role-playing too little is still a part of the Pathfinder system. However, the customization of your character is very impressive in Pathfinder.
This book did what it should for a DM. It filled my head with ideas for things that I can use. The character options are very well done. In 3.5 the primary way that you customized your character was through a prestige class. Pathfinder moves strongly away from that and customization happens with base classes. With the Advanced Player Guide, which I haven't read but will be soon, this rises to 17 classes. That's a great way of defining your character from the start.
There are five chapters, all of them really good. I personally don't think that I will use the words of power alternative magic system, but I think that it will be attractive to some groups. The spells in particular are very well done and very evocative. While the spells are very much combat oriented, they are very thematic. They allow more than ever before, the ability to play a character through their spell selection. They also address things like creating demiplanes and stopping the aging process. There are a mind boggling number of options for characters here.
What is really impressive is how well thought out it is and how much care went into it. Wizards always maintained far too fast a publication schedule and all their books are really mixed bags, often with a lot of dreck in them. This book is just well thought through and contains a massive amount of really good ideas. If you want to do a supplement for a rules heavy role playing game this is how to do it.