This might get a little long so I apologize in advance.
1.) The return of races/orgins for the PC.
As bioware/the df team have no doubtedly heared repeatly, removing origins from DF2 didn't help it. In an RPG, I want to play as the character I envision, not bioware's. If given a choice I would always choose to play as an elf everytime, but its nice having the freedom there to choose what you want to play as.
2.) Customization.
I know this was mention a couple months back, but more customization never hurts. Personally, I'd love to be able to fiddle with all the little details of my characters appearance; like the exact place of a scar, or how long a certain hairstyle is. Armours and weapons need varity, I'd like to see some sort of armour/weapon crafting system that has a selections of templates for each style of weapon & armour then you add your own flair by like altering the length of the sword's blade, changing the weight of the weapon so it swings faster for less damage or slower for CHRUSHING PAIN, alter the fit of armour, like a tailor fitted breastplate or just one that makes you look fat - colour changing is a must!
Or you could have a build your own kinda system, where you can make a sword by like choose from different handles and pommels then style of blade ect.
3.) Decisions that matter.
I think enough has been said on this one.
4.) More classes.
I missed Arcane Warrior as I forced myself through DF2, the classes were very clear cut. It was either you can swing a sword good, stab people with the pointy end of a dagger or hurl magic at them.
I think most people would agree, if they are playing as the hero - they want their character to be that little bit special, like being able to wrap their sword in magic fire before carving a darkspawn clean in two whilst crushing another to death with crushing prison. I would love to see fusions of the classes.
5.) Armoured robes/cloaks/clothes.
Something all too rare in games are cloaks and capes and stuff. To me at least, cloaks just add that little extra touch. And hoods should be an option as well.
Perhaps a fusion of them all, like the character wears a suit of armour but underneath you can clearly see folds of clothes and his cloak flapping behind him as his eyes glow softly from beneath his cowl.
Bonus points.) Proper sheaths.
Please, please, PLEASE - Don't make everyone stick every single weapon on their backs... it's ridiculous, especially when its daggers. One handed and one and a half swords should be sheathed against the waist, same with daggers, big clunky things should go on the back... but that's just my two cents.