i have to say, with a bit of work, multiplayer could be really fun, if you reduce the number of NPC spawns then you replace them with massive player parties running around slaughtering each other, that would be fun. add in a seige option so you can re-create helms deep and there you go!
although, a possible problem is that like wih multi-theft-auto (the multiplayer mod for the GTA games) most people went around doing there own thing and not taking part in large gang battles