Here´s what I am going to say about this comparison between the stories and environments in DA, and hold on, cause it is going to be good, and I am not going to be saying it twice...
The main difference, which makes me think of DA:O as more grey, twisted and provoking is not because of boobs, brothels or blood...it is simply because the evil of DA:O comes from within humanity (or dwarvenity, elvenity or whatever you call it) itself.
The blight is not the enemy, the blight is the symptom. Loghain is a war hero, a self-made man who loses his moral compass due to his fanatical desire to maintain Fereldan independence. The dwarven pretenders are consumed with their hunger for power, and their paragon, who should be the guiding voice of her people, is too obsessed in her quest for engineering mastery that she lost touch with her humanity. The elven keeper is consumed with revenge, unable to let go of past grievances even hundreds of years later and the mother of Connor was so protective of her son that she made him into a demon. None of these characters are evil or morally misguided because of some ancient god, blight or other influence, they are evil because they are human and as such prone to failure...it is all very biblical...
In DA:I, everything comes down to Corypheus...the templars, the mages, the wardens, the duchess, the venatori, Calpernia...it is all because of Corypheus. Sure, they all have their weaknesses and personal desires to make them suspectible to Corypheus influence, but in the end, he is the one who pushes them over the line. In DA:I we know who the big bad guy is, and we know that most of the other bad guys are bad guys because of the big bad guy. Loghain, Uldred, Branka, Zathrian never required some powerful evil influence to make them into monsters, as humans (or elves or dwarves) they already had these monsters inside them. When the real enemy of the story is ourselves, it becomes much more troubling and compelling to us than any monster or demon, no matter how scary, bloody and diabolical you make it.
To me it wouldn't have mattered if DA:O had been presented with brightly colored stick figures moving around in a cookieland, it would still have been a darker story that left a stronger impression because of the inner mechanisms of the story itself.