While MTW was really STW only in Europe with lots more units and a few new features, RTW looks like it is going to be pretty much a completely new game from what I have seen at industry shows and events. While the strategic battle angle will be similar only with far improved graphics and a more intuitive interface, the campaign feature is going to be very different. There won't be definately defined 'provinces' any more for one thing. This should make more fluid frontiers. Whether this is your preference will just remain to be seen. The Roman campaign looks like it will be much more event driven than the laissez-faire style of the current campaign game.
From what I've seen: it's not going to Total War 2 (or 3)