The reason DA:I got so much praise when it came out is that it did something that hadn't been done in a pretty long time, if at all; created an open world RPG with a well written story, that didn't totally lose focus on said story. The addition of Bioware's classic conversations also adds to the whole open world thing a lot, and made it more interactive.
The most recent games even remotely similar before Inquisition that would stick in people's minds would be Oblivion, Skyrim, The Witcher 2, and pushing back an age, Morrowind.
Oblivion and Skyrim suffered from classic Bethesda Syndrome; 3 voice actors for the entire world, between bad and fucking horrid mechanical gameplay systems, an ocean of just... shit, where the main story gets lost in 5 minutes to everything else in the world, bugs out the wazoo, and a whole lot of other issues. They're great for those that love them, but they're lacking hugely in the key areas DA:I is... "Stronger" in.
The Witcher 2 was, on the flip side, well executed, but quite small, consisting of only 3 self contained areas, and without the grand scale of other RPGs. Its combat was a bit clunky, but was at least passable. Basically the opposite of Bethesda's titles.
Morrowind was over a decade old, and while it did a lot of things very well, it also suffered from many of Bethesda's core issues, and had a very different gameplay paradigm from what is accepted today.
When Inquisition came out, it had large, sprawling maps, and a large number of them. If you wanted to explore, you could. Each of these maps was filled with world building, unique characters in most of them, and followed through with the theme of the Inquisition, even if only loosely sometimes. The story was never lost, and was constantly re-inforced, even when you were just dicking around. It was also a damn site better than stories like those found in Skyrim, which got even more praise than Inquisition when it came out. Dialogue was well written, well acted, and usually engaging. Few bugs, combat was passable, not bad, though it did have its issues and was rather bland overall, not doing anything to really distinguish itself.
For all of these things, it got lots of praise. It was a basic, but still decent, version of the different Open World formula that people had been looking for for a while.
And then came The Witcher 3. Take everything good from Inquisition, then replace the bad stuff with more good stuff. After Witcher 3 came out, there wasn't really much praise given to Inquisition anymore, as TW3 had 1 upped it in all fields.
Overall, is it a great game? No. Almost no open world games are, in all honesty. They are ALWAYS marred by sub par gameplay, lots of stupidity with crappy mini quests and collectibles, unfocused stories, and a whole list of faults that really could take their own thread.
At the time, Inquisition was one of the better open world games in near a decade. In some ways it still is, its just been utterly outdone by CD;PR.
Besides that fact, I think almost every game coming out these days could have a similar level of criticism aimed at it, and most of the ones from the old times as well. A lot of it still comes down to personal preference while so many games are so full of faults, and we're still figuring out how to make truly great ones.