This book is great if your a player or a GM, as the tools work perfect for both.
I feel biased here because I love Divination. It's always a chore trying to figure out what a Diviner is supposed to do. It seems like you're job is to either break the campaign by spying on the enemies for the classic scry-and-fry, give everyone in the party a few rounds to buff in combats that were supposed to be ambushes or sit back and watch as your GM sets up anti-divination fields in every relevant location in his campaign. Worse yet, spells like Divination or Augury frequently took a long time to resolve if the GM wasn't prepared to come up wtih a vague premonition or riddle, but I'm pleased to say this book resolves lots of these issues. Combat Prescience gives the diviner a buff most martials will drool over (you could even build around it yourself). Lore Delve and Detect Conjuration give us two resources I'm shocked weren't already in core (a good sign). And Mirror Sight's detailed scaling and limitations gives us the perfect "scrying sensor" that at higher levels can be used as a fascinating encounter or intrigue tool (I want to use it as a GM!). But my favorite spell in theb ook was Hypothetical Scenario! Giving players and GMs alike this pseudo-augury that let's you play out the potential results rather than trying to guesstimate or hide it behind some riddle or prophecy is easy to manage but still dripping with flavor. The time limitations of the spell ensures it won't break a campaign, and the way in which information is disseminated gives whomever casts it a number of ways to theme it's resolution.
[5 of 5 Stars!]