It's not really what I would consider a "fully new" TW game thus I don't expect it to be THAT buggy. Sure it will probably have some bugs but I doubt anything game breaking , it's being built on the foundations of Rome 2 which is actually a pretty solid now after all the patching they had to do to that, so they would have been able to focus a lot more on the new features they have added. It's going to be a far smoother release than any other of the major titles, more similar to what Napoleon is to Empires I imagine.
Still, personally I was hoping they were working on something else rather than this lol.