Well, first of all, I wanna say that I loved Dragon Age Inquisition (I expected it to be better, but it was stil awesome). I've been a Mass Effect and Dragon Age fan since 2011, and they are my favourite sagas (altough I'm able to admit that they did many things wrong) 
I'm on my third playtrough now, and I feel the same way as you. The game feels... Empty. You have amazing maps and places, but nothing to fill them. Did you see The Hissing Wastes?? It's huge! The biggest map in the game and it has, what, 20 missions? All of them side-quests of collections. Same happens with the Fallow Mire, you bring back your people and that's it, the rest is empty.
The worst part is that you have no reason to do the quests (unless you're playing in Nightmare and you need to level up), and you may miss a huge part of the game (by that I mean gameplay hours, not important content), just because it's "not important". And, let's face it: playing hours and hours, doing silly side quests so you can move on into the story, simply sucks. What happened to the fun? To that "I wanna do everything" feeling?
In Origins you never knew what was part of the main story, because everything felt so damn important and awesome that you did it anyway... It didn't feel like "side quests", it felt as if everything was part of the main story. It was awesome.
Still, don't get me wrong, DAI was really awesome, and I liked it. For example: the companions are awesome, some other characters (such as your advisors) are also great. They feel real, they have their own stories, personalities and they feel like people. The romances are beautiful as well, and they feel real too. So was the music (amazing as always), and the enviroments, and the designs. Skyhold was a badly done (it's never rebuilt, your upgrades don't seem to matter, etc), but the design of the castle is both breathtaking and beautiful.
About the combat, I like it a lot: it's faster, the barriers and guard are awesome, and it's a lot more fluid. The only things I dislike are: the auto-combat option (now solved with patch) and the chance to assing atributes.
I missed the cities, too. I thought Val Roxeus was going to be amazingly huge and that we would be able to visit all those places we see in The World of Thedas, or read about in The Masked Empire. But nope. It was a tiny, tiny map, with no sidequests or whatsoever. So sad... It was our big chance to visit that pompous and foreign Empire we've heard so much about.
About the main story, it was simply gorgeous, but it had some really bad things. The biggest one? It takes too much to "begin". For me, the story really begins when you get to Skyhold. Usually, games are pretty straight-forward until the story really begins, for obvious reasons that DAI forgot: we get distracted.
If you do pretty much everything, it can take you about 50hs to reach Skyhold. That's just wrong.
Another thing: the main gold is to defeat this Elder One, and the guy shows up like, what, three times? Think about Saren, of Mass Effect, the guy appears a lot, we know who he is, why we must stop him and when we do, it feels amazing. With Cory, I felt nothing, just this "it's done" feeling and a strange feeling of emptyness. Nothing more. That was pretty sad, I mean, where is the big battle?
Who is this Cory guy? Ahh yes, that misterious guy we've been chasing for the past 90 hours, I remember now.
Well, that was long! Sorry, I never thought I would write so much; I'm just a Dragon Age junkie
