A little over a year ago, Mike introduced me to the Incarnum system from 3.5. This was just before we started playing Pathfinder almost exclusively. He explained to me the absurdly complex system by which the classes functioned. I was hesitant about it, as I'm not too keen on having to balance and juggle three different pools at once. I promised Mike that I'd try it, as he was really big on the system and what it could do. I tried it on for a couple sessions and decided I hated it. It wasn't for me, too much micromanagement for my tastes. I ended up focusing so much on moving my essentia around correctly that I completely missed what the party was even doing.
It's that experience that Mike hopes to eliminate with this adaptation. Magic of Incarna promises to broaden the scope a bit, making a powerful and complex system that is still accessible to players, like me, who can't handle the minutiae the original system relied on.
What has emerged is an interesting and varied document. Players will discover a new twist on the traditional magic systems. It's a different way of looking at magic and how it behaves in items, in characters and in the world around them. The first document includes the Vizier, an intimidating manipulator and combatant, capable of creating powerful bonds with magical items.
Being a playtest document, it should be stressed that what you'll see is not a finished document. Some things will likely be tweaked here and there. If you decide to participate in the playtest, your feedback is essential to improving the document as a whole.
From what I've seen, it's a strong system with a lot of new and interesting options for players. It's certainly far less ungainly than the system Mike introduced me to a year and a half ago.