When it comes to dark and gritty, one must understand that this is an expectation. An expectation that has most likely, increased due to the popularization of series such as Game of Thrones.
Additionally, one must remember that the Dragon Age franchise itself, started off with a very Game of Thrones vibe to it. There was family betrayal, family slaughter, rape, corruption of a dear friend, friend using forbidden arts, wedding gone wrong, citizenry enslavement, caste system, sexist philosophical system (that was conveniently whitewashed in DAI) and what have you.
Dragon Age Inquisition felt like generic fantasy RPG and that's it. The previous generic fantasy that came out before Inquisition was Skyrim and even that game had the sense to be dark when it came to its Daedric quests, vampirism, lycanthropy and one of its guilds.
These days, when people think dark and gritty, the probably do not just expect some alternate universe shenanigans and be done with it. They want a violent family massacre like what happened to the Stark family in Game of Thrones or the Cousland family in Thedas or perhaps a very manipulative and scheming ****** that double crosses everyone to get what they want or some dastardly political intrigue. They may also want a world where the art complements the dark and gritty setting.
Dragon Age Inquisition does not have these moments in almost every aspect of the game.
1) When it came to Origin stories, you did not suffer a massacre or backstabbing that made you flee or original family and end up in Haven or you were not victims of assault and abuse by Templars and Mages, something like Tabris suffered at the hands of Vaughan in Origins. It was a few sentences and a war room mission or two.
2) The creepiest crap that the game had was the big spider thing which we did not fight yet we have fought and killed creatures the likes of the Broodmother and the Harvester and even the Varterral. Poweful bosses like High Dragons feel powerful but they never feel like they are going to tear you apart.
3) The art in the game is bright, colorful and cheery even as opposed to dark, gloomy and gritty. This is perhaps one of the biggest issue with why the game does not feel dark and gritty.
4) The gameplay is too over the top as opposed to being violent and brutal. This follows right behind the art not being dark and gritty. You do not really get the sense that you are popping heads with your arrows or chopping people into pieces of meat with your blades or roasting them alive with mage fire. The gameplay is all about being flashy, being spammy and nothing else. If anything, I actually somewhat like the Team Fortress 2-esque violence in Dragon Age 2's gameplay.
5) No one you really care or grown to care dies in the game. Roderick is Udina 2.0 with some conscience and let's face it, he is neither our follower nor our adviser. We did not have a Virmire situation with our own companions. You could argue the Hawke vs Stroud / Loghain / Alistair is dark but they do not involve our characters. I mean we have nine of them this time. Nine.
6) The loss of the Crestwood demo thing. I think most of us enjoyed the timed mission for the Crestwood demo back in the day. That was cut out and instead we get a rehash of Origins' Redcliffe.
7) Coryphefish does not do much apart from destroying Haven. He never tried to setup an elaborate trap to corner you somewhere or did not kidnap and hold someone you held dear for ransom (alternate universe does not count). He didn't do much.
8) The followers. Out of the nine, only Vivienne was the one with an actual secret agenda but that was never fully fleshed out. With Morrigan in Origins we had her Old God Baby, with Anders we had the Chantry explosion, with Isabela we had the theft of Koslun's Tome. I suppose Blackwall's masquerade was something but come on, there were nine companions. I expected one to be a spy planted into the Inquisition to report to Corypheus or something.