The MP part of AC is the part that worries me most. All the other main elements (physics, graphics engine, sound engine, UI, content etc seem to be of extremely high quality.
Programming the netcode for a game has never been Stefano's strongest point. In namie it was quite below average and the netcode of netKar Pro (what's in a name) is still not up there with rFactor or iRacing (for me iRacing's netcode is amazing).
I hope Stefano got some help with the netcode or improved his netcoding skills a lot.