I really hope Mount and Blade 2 is going to be dramatically different than the previous games. I mean, the base game is there now they just have to develop it further along. The main appeal of Warband for me was the graphical improvements, but there wasn't to much else that was appealing outside of some other minor enhancements. I won't even get started on Fire and Sword.
1.) Sieges need to be completely revamped. Whoever thought it was a good idea that an army of hundreds would use one ladder is a bit loony. They need to let you use more siege equipment such as battering rams, catapults, ballista and even more siege towers or ladders to use. If the walls were destructible, that would be fantastic too. Rather than building the siege engines like catapults there, you can have them constructed in the city, castles, or wherever else and they dramatically decrease your travelling speed to balance it out.
2.) Better battle AI, so battles aren't just a single mosh pit and the implementation of formations. Modifications have created this, so the company should be able to provide more tangible battles rather than a concert party. In addition to a battle use for the tactics skill. As in, so many points should give you a deployment zone (Like Total War) and let you pre-arrange your men on the battlefield rather than having to use the lackluster mini-map for this or having to go there yourself.
3.) Naval battles are one of my favorite features that have been modded in and there should be a variety of ships that you can build to engage in naval battles with. I think this would add a whole new dimension of activity for people to engage in, rather than the same land battles over and over.
4.) Advanced kingdom and military management as the current system is rather simplistic without much appeal. Again there's been modifications that have added new features and elements of immersion that should be included.
5.) Outside of the illusion of having to manage your army with food and payment every week. I'd like to se the capability to personally equip your soldiers with weapons, so if you're poor, their weapon quality will reflect that. However if you're wealthier, then you'll obviously be able to afford better equipment. This can be applied on a mass scale for units, rather than specifically like for companions.
And that's generally what I'd like to see the most for Mount and Blade II myself.