Well, regarding DAI, my greatest problem with it was that in most of the zones you did nothing of note. The justifications for going there were weak at first and as we cleared the areas, well, there was nothing there that needed me. Inquisition troops could have done it all by themselves.
It does feels like a shallow mmo, and tbh my expectations before launch were from an mmo. I wanted the optional areas to feel like SWTOR, to have an storyline of their own just like each planet had one that worked aside the main storyline of your character. That's what I loved about SWTOR, I can have my SP while going along with a friend, and the planets offered a coop story for us to do together.
Aside from that the chapters or missions in DAI are fine, the problem is that as a whole they don't work together. The pacing is horrible, and that's without taking into account the hours that can be between main missions. By this I mean, that after you get to Skyhold the story looses all tension and the only thing it progresses is the gradual revelation of Corypheus as a joke. The great mastermind with so many troops and agents to be on so many places and it gets thoroughly defeated every single time except 2. One because you weren't there (mage and templar missions), and the other one is when he marches on Haven, the only move in the entire game in which he seemed to actually take his plan seriously. After that second act we get our climax, with big lore revelation on top. Genuine yay! What do you mean there more? You mean the epilogue? Like the party at Denerim at the end of DA:O?...Final boss fight?...oh right Cory...

So it turns out Cory is actually powerful and why didn't he just lift Skyhold and drop it? Why didn't he use all that amazing power to just crush us? Oh I guess we're ending and the true villain was Solas. Ok.
And this might be personal but the gameplay was just boring, and attemp to make it more like a CRPG but without implementing actual CRPG mechanics.
Is it a horrible game? It's ok, but it's worse than its predecessors (yes, I prefer DA2, even with its third act beating you on the head with Mages and Templars).
So if they're going to have a focus on exploration for ME:A I'd rather they take a different approach than DA:I. Put interesting sidequests that compells us to explore the map. They don't even have to take place in cool areas, just something like in the way to complete that sidequest we may see something that draws our attention, hinting other interesting places in the map. Or, here's an idea, we could go explore the whole map, then get the sidequest and hey, we have inadvertedly completed some.
I don't need everything to be full of content, the desert map at night in DAI. I would have prefered actual bioware storyline with the reason we go there but I'd leave the rest as it is, even if there are large expanses without anything. Why? Because it was highly atmospheric, and you could actually see points of interest to go to. With this said, I think it won't come as a surprise that my favourite area in DA:I is Descent (technically several, but I count it as a vertical, singular area), if only the last seconds didn't ****** me off.