Nightmare difficulty might be its only saving grace, imo.
I´m playing it on nightmare (archer, party at level 6 atm).
It is its saving grace in terms of difficulty - so far it´s been rather difficult, quite a bit more than nightmare in DA:O.
In some encounters I was forced to various retreat tactics (running all over the map), and there were few fights I had to postpone for later.
There´s a good amount of problems though, mainly:
a) encounter design sucks
The game uses the "waves" mechanic all the time (in about 95% of encounters).
You start fighting against one group of opponents, once some are killed another group joins in (they often simply materialize out of thin air) and sometimes even third appears.
From time to time, this would work well as an element of surprise with a good potential biting player in the ass if too many resources were wasted, but having almost all encounters like that is a bore, in most cases feels unnatural and makes encounters more tedious than challenging.
b) applying AoE´s sucks
First, when using AoE abilities/spells, only enemies affected are those who are in the area of impact the moment the ability/spell "impacts", not the moment when it´s fired (as was in DA:O) - this makes firing AoE´s completely action-y and, given the overall speed, very unreliable.
Second, the targeting of AoE´s themselves is out of whack - the target circle keeps jumping around and you´ll get it only rarely in the exact position where you want it to be, in more confined areas (which the game uses rather often) it like, doesn´t work at all.
Third, camera is woefully limited, adds yet another layer to AoE suckage and, again, in more confined spaces it´s total ass. Absence of tactical view is a HUGE minus.
Obviously this is bad on all difficulties, but on nightmare where good positioning is crucial, this is inexcusable.
I´m not exaggerating when I say that half of the challenge comes from fighting with these three aspects.
I quite like DA2´s nightmare difficulty on paper (enemy immunities, party members bleeding to death when under 10% of health, rogues stealing party´s potions, enemies being affected by their friendly fire as well) and it blends well with some other changes (long healing spell cooldown, long cooldown on chugging potions, etc) but due to major control issues and repetitive, uninventive encounter design it just doesn´t work well in practice.
It´s pretty obvious the game was designed as action-y hack´n´slash and doesn´t lend itself well to the challenge nightmare is trying to provide.
As for the rest of the game, mediocre so far, though I´ve yet to see some major character/story development since I was mostly exploring the optional stuff.