I think what went wrong most in DA2 was the gameplay. Too many trash encounters, too random difficulty, too many side quests, and for gods sake, whose idea was it to remove auto attack?
The story was random as well, Act 1 was side quest extravaganza and a decent main mission in the deep roads (I still wish we could have found out more about that thaig). Act 2 was kinda meh, all plot twists were predictable and nothing really stood out. Act 3, however, was bloody fantastic, some things actually had me shocked, but it ended too fast, in fact, the whole game could have just started at Act 3.
Anyways, I'm anxious to see DA3 and the conclusion of the conflict that just started in DA2.
However if they do want to fix it, gameplay needs a complete new revamp and they need more focus on the story missions and less focus on side quests.
Also, in my opinion it would be great if the game finally went continent-wide, i.e., not just limited to one country per game, but being able to travel to locations in each one of the countries. I'm dying to see the Tevinter Imperium or the Qun'ari lands but so far we didn't have the opportunity.