Stuff that I really liked from DAI was
The Battle of Haven mid-way. from start to finish, including the song and discovery of Skyhold. It was a great reveal of the main-badguy, it had tension (try to save everyone), drama (Roderics death, Quizzy standing up to Cory etc), a sense of urgency (again villagers, defending the trebuchets), a little sense of victory when you confront Cory and escape, than the emotional peak when in the camp, everyone is singing etc
The templar/mage-missions were also cool, with one taking us into a trip to the future, and another in into our own mind confronting a dark entitiy within, showing us how the world could end like without our intervention. At least the latter could somehow be made in ME as well.
The temple frozen in time was also really good enviromental story-telling and visually so great - I hope MEA tries to tell more side-quests this way (additional to dialogue and cutscenes). Finding places where looking around, seeing remains, ruins, etc tell us what happened here, without much need for too much exposition
What should be avoided? Too much "open world"-criap. Yet the MAKO-Return already gives me not much jope on that part. Open world and exploration nowadays mean radiant repetitive "quests" that are merely there to waste our time with work instead of play ...
Also over-abundance of crafting...I just do not care about crafting. Finding ressources, and diagrams, and then you craft something, but then you find another better diagram, but you do not have the ressources anymore, so you always end up not using anything because you might find something better etc. Crafting is my least favorite thing of modern gaming ^^
But most of all: Keep the story "tightly narrated". Have the villain a constant threat, have us interact with him, show us why he IS the villain we should take serious. In DAI Cory all but vanished after Skyhold, and we hardly really see why we should fear him. Let the villain's armies march, plunder, pillage in cutscenes, let us face them and FAIL to save the planet/city, show us locations filled with refugees or whatever. And not just once - often, to create a sense or illusion of urgency while we runaround with the Mako scanning minerals - I go so far as: give us missions that we MUST do and cannot delay ecause damn, its super-important to stop the baddies NOW and not after we strolled over planet Pointless for 12 hours ...