I'd like to see a few things in DA3:
-More specializations (Mage perspective). In DA2 I felt confined when picking specializations because, primarily, I disliked playing a healer, so Spirit Healer wasn't much of an option for me. Playing a 'Good' mage also blocks out blood mage for me. This leaves Force mage, which isn't bad, but it was the only one I felt I could pick, keeping in line with the type of mage I was playing. I think it would also be cool if some specializations incorporated other classes too, like Arcane Warrior in DAO, and have specializations such as Arcane Archer for Rogue or Spirit Warrior for Warrior, or a tanking type Rogue which focused on their dexterity in dodging attacks, while keeping aggro. This would make it a lot more interesting and would allow more free reign on the type of character you'd like to play. I say this because I loved the way mages attacked in DA2 (it felt awesome) and I loved the staff/swords/clubs etc that you could have, but when you used the weapon end of the staff on a close enemy, it was a little disappointing to hit next to nothing and have to run back and cast, instead of having a warrior/mage combined specialization and being able to deal damage close up, and from afar
-Bring back spell combo's/add warrior and rogue combos, not just cross class. This was a good idea to have in DA2, but I still felt the spell combo's in DAO were a lot better; there was nothing more satisfying than conjuring a Storm of the Century in the middle of a large group of darkspawn. I think it would be cool to bring these back, but somehow incorporate combos for rogues and warriors too.
-Ability to visit different places. Don't get me wrong, I did like DA2, but playing DAO again made me realise how much I loved visiting different areas, different races, learning about each race's culture, government etc. You did visit races in DA2, but I felt it was a lot less focused upon than in DAO. Granted, you could read the Codex pages for info on this stuff, but personally, I prefer to be involved with whatever I'm learning about, and I only really read codex's if there's something not directly within the storyline, just lore.
-Combat variations. Like I said before I loved the way you attacked in DA2; rogues actually felt dexterous and speedy, warriors felt strong and powerful and mages felt awesome flinging their staff around like some kind of monk. The only thing I'd like to see improved would be to add variations the the animations of combat. It would be even better to have 2 / 3 different default attacking animations rather than just 1.
These are the main things I'd like to see. They are all from the perspective of a Mage primarily as you could probably tell, but I have played the other classes

. There are other obvious things that everyone seems to want (e.g. no more reused areas) but those never seemed to bother me as much. Yes, it would be better without, but It doesn't make much difference to me personally.
I'm looking forward to what DA3 will have to offer!