As far as melee goes, I'd love to see the original weapon types brought back(Obsidian, Master, etc.). Also, dual-wielding would be sick; I can just imagine hacking away at a Balverine with two Cleavers.

Maybe holding two of the same type of weapon could add damage bonuses? Without getting too far into the realm of Diablo, Weapon/Armor sets would be badass. Once you got every piece of gear within the set, you receive more experience per kill, more damage, etc. Combining melee with magic would be crazy as well. Like someone said above, only with weapons instead of your fists. Charging up a Greathammer with Fireball or Lightning would obliterate anyone!
In my opinion, Ranged combat was great in Fable 2; I don't really see much room for improvement, with the exception of the Sets/Charging things I mentioned above.