So, my initial thoughts? It's a cross between 3.5 and 4th. Knee-jerk reaction is that I like it as it seems to take the best elements of 3.5 for players and the best elements of creature and encounter design from 4th. I'll have to pore over it for a lot longer but so far, it already feels like a step in the right direction. It feels comfortable, familiar and streamlined.
The fact WotC is letting its legions of fans playtest the next version just thrills me. I wish I could shake the hand of whomever had that idea.