In my view, DA is ‘slightly darkish’ and ‘occasionally tries to be mature’. Which is more than most videogames can claim.
I’m with those who consider ‘maturity’ in storytelling to lie in realism (not literal realism per se, but credibility in terms of behavior and motivation) and complexity. Complexity meaning the intricate web of various actors, motives, events and relationships that exist (or would credibly exist) in the context of the story. This is, of course, as far as the medium allows. For instance, a complex historical situation may be condensed and simplified in a historical novel, when compared to a major study about the same subject. A (high-quality) TV series based on the book may have to simplify things even more, and in the case of a movie that gets even worse.
In that sense I totally agree with Alan that ‘mature’ does not have to be ‘dark’. You could have, for instance, a story centered on dynastic politics or a diplomatic mission or a voyage of discovery with little or no rape, torture etc., but which is highly complex and fairly 'realistic'.
Apart from the whole question of how to define ‘dark fantasy’ (see Is Dragon Age Inquisition dark fantasy?), I personally would describe as ‘dark’ events and situations that, from a modern western perspective, are morally beyond the pale. Deadly violence between combatants in war, while they may be depicted in a graphic manner, is not really dark. Consensual homosexual acts, on the other hand, would not be a problem (let alone ‘dark’) in the perspective of liberal westerners, but their not-so-liberal neighbours and relatives might disagree; our great-grandparents would be horrified, and their great-grandparents would find it right and proper that homosexuals were publicly executed. The depiction of consensual sex (out of lust, love or for payment) is also quite divisive; I sure hope nobody thinks this to be ‘dark’ but given my nationality (Dutch) I may not be representative in this regard. At least everybody will agree about things like torture, rape and genocide (I hope…).
Any ‘darkness’ in terms of violence (rape, genocide, torture etc.) can be both graphic in nature and mature provided it makes sense in the context of the story that is being told. A movie about an inquisitorial investigation (like Ken Russell's 'The Devils') would not be what it is without the scenes of judicial torture to which Urbain Grandier is subjected. On the other hand, a movie about the inquisition solely showing pretty girls being violated…well, let’s just say the maturity of the movie in question would be more than a little suspect.
The same with movies that deal with particularly horrific aspects of World War II. The more shocking scenes from Schindler’s List or Andrzej Wajda’s Katyn (about a notorious Soviet mass murder of Polish POW's) have a very explicit purpose, and while they may ‘shock’, shock itself is not the point. Rather, driving the point of what happened home, ‘de-clinicalizing’ what might conceivably have been kept offscreen. It’s not the only way you can do this – the 1984 German movie Die Wannsee Konferenz' (the same event, a secret conference about the implementation of the 'Final Solution', was also the basis of the movie ‘Conspiracy’) totally delivers on the dark and horrific without a single drop of blood – but doing this well depends on using the right combination of context and narrative techniques.
On the other hand, ' Ilsa, she-wolf of the SS’, while also showing horrible scenes of violence in the same general context…is not so ‘mature’. The setting is merely an excuse for an exploitation movie featuring nudity, not-so-consensual sex and sadistic torture.
A lot of fantasy, somewhat unthinkingly in my opinion, simply presents situations and conflicts that, ‘realistically’ would not just have been really, really horrible, but would have been witnessed by the player characters first-hand, but this is stuff that is mostly kept from the player. At best, you see a few ‘lite’ scenes with a bit of blood (not real nudity, God forbid!), mostly copied from similar (but often better) scenes from popular movies. They are flirting with potentially ‘dark’ subjects but are unable or unwilling to commit to bringing this actually to life within the game, visually or not.
Take DA:O. The Blight basically means extermination for the entire population of Ferelden and the ecological destruction of the land itself. The heroes travel through Ferelden, but rarely see anything of it, except for the occasional (in terms of impact very ‘clean’) couple of corpses or a sacked town.
In DA2, Kirkwall was depressing, but this had less to do with the dire circumstances of Ferelden refugees, local Elves or the Mages, and everything with excruciatingly boring and repetitive visuals. You never really got a feel for the desperate conditions of the poor, the elves, the refugees etc. There’s a bit of it, but generally rather clinical-looking and not really convincing in any way.
Both games did have moustache-twirling villains (even if they were not major NPC’s, with the exception of Howe) though, moronic and / or insane antagonists, silly sex scenes, Whedonesque comedic banter and bloodsplatters up the Wazoo and brown (darkish brown in DA:O, tan brown in DA2), oh so much brown. But then, as so many games (and quite a few movies and tv series) have proven time and again, brown is dark AND real.

And you know what? That is quite alright and I don’t mind it too much. I have other places where I can get my ‘dark and mature’ fix.

But it also means that, if the DA games are intended as ' dark' and 'mature' they don't get anywhere near to succeeding in it.