The last--complexity. Complexity is probably a bigger barrier for
players unfamiliar with traditional RPG's. It's not clear to me that
older bioware games were more complex--they were in some ways (more
spells, more classes), but non-magical combat was far simpler under
AD&D rules than DA:O. Complexity can support roleplaying in
enabling someone to customize their character...but it can complicate
the difficulty question. Simply put, the more abilities you have, the
more susceptible the system will tend to be to min/maxing.
Complexity in an RPG is much more then simply the number of spells and classes you have. To me D&D is no more complex then DA:O, it's much more refined due to the couple of decades it's got over Origins but in reality they are very similar systems with about the same amount of complexity. To me complexity is the amount of depth within the various systems; the combat mechanics, the character development on a stat level, the class system, the loot and reward systems, ect. Dragon Age implemented these of a very basic and shallow level, but it's really no different then any other BioWare game in the past. BioWare games really are about as simple as they can get without becoming something like a Diablo with a story, though I suppose the Mass Effect series has fallen within that rank. It's not a knock on them at all, I'm just simply surprised that people are worried Dragon Age might get "dumbed down", it's already built fairly simple.
Some people will--for roleplaying reasons--want to
make non-optimal choices. If the game is not playable for them, it's
not a good RPG. I confess while I'm as hardcore as they come on some
issues, difficulty is not one of them. I hate being forced to min-max
or play in a style I don't enjoy to get through a game and I've quit a
number of games for that reason--System Shock 2 (mentioned by another
poster) was one of them.
Difficulty is no doubt a touchy subject due to the wide variety of the audience and play styles. But personally there was very little challenge in this game even nightmare, and I'm still completely shocked at threads I see complaining normal is to hard. The AI is incredibly dumb, but as you said AI has always been a weakness for BioWare, the lack of eveny types results in deja vu effects, what you did to defeat that last group of Darkspawn will almost certainly work on the next one considering they are almost always composed the same number and types, they have nowhere near the arsenal of talets/spells the player and their companions have which gimps them even more, they lack the ability to consume pots(?) while the player/NPC's have no restrictions aside from self imposed, and there are never any curveballs thrown in to force you to change your strategy mid-battle.
I understand the need to avoid forced powergaming, afterall half the fun in the game is building the character you want. But I don't think the difficulty Nightmare should be the breeze it is and I'm certainly no powergamer. Let's not even step into the realm of Awakening.