This has been a long time coming, but the need to try everything out trumped review attempts.
Let's get the negative points detailed first:
A great deal of the book seemed to just exist to "test the waters" and lacked clarification. I hope this won't be a standard practice, as it hurts the new material introduced. Editing mistakes were very obvious in the first printing, which gave the book a faint 'rushed' feel. The Words of Power variant can be useful in some playstyles, but generally won't see much time at my table. While the approach is fairly balanced, it's also weaker (with an already weakened class type)and I did not like the sacrifices required.
None of this compared to my utter disappointment when I realized that seven pages were devoted to sample spellbooks. I will never use these and feel that the 'preparation ritual' boon (and suggestions on how to add them to existing spellbooks) should have been the focus. This reminds me of when WotC began introducing old monster races with class levels in new bestiaries. The focus should be on the mechanic, not on examples of the mechanic.
Now for the good stuff:
The magus is exactly what it needed to be, despite the odd name choice. While the spellbook requirement is an ongoing problem I'll ignore for the moment, the only immediate fault I can find with the class is very limited spell list.
None of the archetypes were a disappointment and quite a few really set my imagination alight. Arcane discoveries are easily my favorite class option and I encourage Paizo to publish more. The new familiars were welcome additions along with the construct modifications. The feat section addressed pressing concerns and needs and I'm quite content with the remainder. As for the new spells, I'm pleased with the majority (95%) in spite of the lack of 0-level spells.
Summary:
Very rarely is hype surpassed by reality and this is just another case of that combined with limited space. The negative may seem to outnumber the positive at first glance, but it's still a damn good book.