The next release is supposed to be more of a stand-alone expansion, trying to be a bit more heavily narrative rather than the completely open world of the original games. Otherwise Warband is pretty much an improvement in every department for around the same price with an extremely active mod community of its own as well, since it's essentially the exact same game as before only improved. There's no reason whatsoever to buy the original game now except perhaps for some of the older mods available for it. Mount & Blade: Warband is essentially a re-release version of the original game plus multiplayer and some new content and tweaks.
