I think this book went to print too early. I expect a couple of hundred clarification/FAQ threads and errata on this.
It seems to me that this is a new toybox with no consideration for balancing the material with what's come before. It's a 'splatbook' in exactly the bad sense of the 3.0 splatbooks. Stuff in here - if incorporated into your game - so far overshadows core features that it becomes 'must have'; essentially >the< litmus test of broken.
The "rule of cool" is one thing. But how about we keep a measure of balance in the game?
I think there is some good material in here, but in multiple places the execution is IMO lousy.
There is no visible attempt to keep it even in balance with itself, let alone core rules.
You may justifiably argue that martial classes need a boost, but e.g. cutting all missiles, boulders and attack-roll spells out of the air for a mere attack of opportunity isn't ever making it to my table.
Nor are gunslinger targeted shots with whatever weapon you like.
Nor indeed are multiple readied attacks in one round, or a saving throw penalty for hitting with an attack. And no, no Vorpal-equivalent ranged weapons.
The first rule of fight-club should be you do NOT mess with the action economy. The next should be 'saving throws and melee attacks are NOT equal'(ahem, Hindering Shot).
This could have been great. Now I have to rule stuff in or out on a case-by-case basis. Seriously disappointed.