He's a classical n°10, build in the same mold than Zidane, he's tall and very solid physically for a playmaker, even if he is probably less creative than Zizou, you won't see him do the kind of crazy tricks Zidane does, but everything he does is intelligent and useful.
He has great vision, a high workrate which allows him to play sometimes as a defensive midfielder, great distribution and can control and strike the ball with both feet with equal effectiveness. It's always hard to take the ball away from him and he looks elegant on the field, in that aspect he reminds me of Fernando Redondo. What else, he may be a little bit slow (at least slower than Kaka, though it doesn't say much), and seems to be a nice guy outside of the pitch contrary to other young french players.
Overall it can be a great signing for Milan, he's definitly one of the 3 most talented young french players today. Now it remains to be seen if he can adapt to a team and a championship of that level at his age, cause he's still really young... Too young IMO, but we'll see.