1. No dialogue wheel. It was shit. I hate it in ME, I hate it here. I want to be able to make a choice without being told 'this is what your choice will do'. If I want to kow what it will do, I'll look up a walkthrough. It makes it that much harder to RP when your hellbent on following a certain path. DA:O, I thought I was following a path, but many of my dialogue options told me I wasn't, like joking with Alistair calling him 'Your Majesty' or whatever at Redcliff. Also taught me how little I actually knew his character. I thought he might somewhat chuckle at it, but instead he seems somewhat more depressed. Taught me more about him, and added depth to his character. If I had of had an option at the top right of the wheel that would have me say the exact right thing to him, I would have picked that over the witty response simply because I wanted to be in his good books.
2. More Dialogue options. Not just 3, a witty, a nice and an ass response, though the first and last could sometimes be put together... I preferred having multiple options that weren't necessarily black white or grey, and I had to understand who I was talking to to make the right choice, not just pick the obvious one that stood out among the rest (Though there were some of them in Origins too, nowhere near as many though). Yes, this would make it harder to voice over, but IDGAF. Gameplay over being able to hear what is not my characters voice any day.
3. Let us pick what we want to play as. Shoehorning us into humans was a very bad move, especially after Origins. Humans have always been the asses of the DA world, and it would have been nice to have been able to be an elf, or a dwarf, and have all those humans look upon you with disdain, and all of your kind be nice to you because you knew what they were going through.
4. No button mashing. Pick a target, attack it, and it will keep attacking for you. Gives you more time to worry about picking your next ability to use, observe the situation, and it doesn't make you fingers ache. Something WAS needed to speed up the combat from Origins, but button mashing is not the way to do it.
5. No respawning enemy waves. I hereby order the death of whoever thought this was a good idea. Pre-placed enemies worked far better. You could see them coming, you could lay traps and plan an assault, it became more tactical then 'Oh look, enemies, lets button mash until they spawn behind my mage, then run over there and button mash until they stop spawning'. It also makes little sense for enemies to just appear out of nowhere.
6. More areas. Don't just make Kirkwall bigger and more interesting, add more than the two dungeons other than Kirkwall you had. For a good example of how things can be done in a small area focus, yet still with a good number of different areas, see DA:O Awakening. Set in one small province of Ferelden, and mainly focused around two towns. Your quests, however, took you outside those towns to view the surrounding countryside, something Kirkwall was severely lacking. I'm sure it would have had at least some interesting areas around it, so why not let us explore them?
7. Give it an actual overarching story. Yes, Hawke rises to power. Wow. My Warden became the greatest hero Ferelden has ever had, rising from a simple city elf. That is a rise to greatness and power, but he actually accomplished something to get there. He defeated an entire Darkspawn invasion almost singlehandedly, with the exception of a couple of companions. There were some slightly interconnected plot lines, but they were just very vague one act, the whole point of the next act, then completely forgotten the act after that. But hey, maybe that's what happens when you jump in years between acts... so, to fix that:
8. More acts. Add more time into the story, so that the vague idea of the Qunari invasion and Mage v Templar subplot-turned-major thing can actually develop over time, rather than just a 'BAM' there sort of thing. Also would have meant that 9 wouldn't have to cram so much conversation into one meeting.
9. More dialogue. You jump years between acts, you would have a LOT to catch up on, so why not talk about it all with your companions? A few short talks is not enough to cover years of ones life, why not have the option of asking. In origins, I could find out a lot about the backstory of all my characters, and the good 20-400 years of their life was bought out with a fair bit of dialogue. I learned about Leliana's Orlesian upbringing, about Sten's people, about Alistair being a bastard child and having never met his sister. Every little thing doesn't need to be included, like 'I woke up and had eggs that morning', but for some of the most important and interesting people in Kirkwall, I'd think they'd have more to say.
10. A better ending. An epilogue more like Origins, where it left plot threads open where things could change, the sequel could continue them, there was more left to be said, and, in many ways, I'm guessing this is what a lot of Origin fans were hoping the sequel was going to include: Something to tie up those threads left open in a semi-cliff hanger. What happens to my Warden after he goes through the portal with Morrigan? What happens to his companions? Do they succeed in their quests? Do they fail? There was a bit of this in 2, and I do like the shift in story somewhat, but more couldn't have hurt. And also...:
11. Don't retcon player decisions. If Leliana or Zevran are dead, don't bring them up. Just... Don't. And if you do, admit it was a mistake, then try to explain it with DLC or the sequel (Mass Effect Conrad Verner anyone? Apparently there is a chance he just had 'a bad day', that will be explained in 3. Apparently), DON'T just say to the fans 'Sorry, you're wrong. Oh, you chopped of her head? Well she lived through that. Or, better yet, you didn't actually chose to kill her! Sorry!'. One of the stupidest moves they made.
That is my short list... for now. I may have more to add in the future though.