As surprised as I was of seeing any news about it, I was even more surprised when they detailed what it would looke like:
a "much more cartoony look to the whole thing; think bright colours, new lighting effects and a visual style that's not a dissimilar from that of hit Disney movie The Incredibles"
Certainly a style break from most FPS games, maybe for the better? What remains to see is if they managed to do some innovative with the gameplay. According to Steam News, they are releasing movies for TF2 and Portal next week.