Da2: I did 2 runs, one on hard (mage) and one on nightmare (shield warrior) level, and I've found both of them harder than Dao (though sitll far from unforgiving).
Reasons being:
1) Gameplay mechanics: during most fights, there are several waves of mobs spawning out of nowhere, and you might end up totally zerged. Best tactic I've found is to lure the first mobs away from the spawning area, to have the time to bring'em down before the others can arrive.
2) Almost all mobs are highly resistant or even immune to this or that element, thus causing your mages to dish out zero dmg if they use the wrong elemental staff. But there's no clue ingame on which element is which mob immune to.
3) Mobs oneshot abilities. Those pesky assasins can kill your non warriors companions wiht just one hit, so aggro micromanagement and crowd control abuse are mandatory.
4) Very low dmg from area of effect spells, unlike Dao. They are just a waste of mana.
I admit I din't go for the "ideal" party setup, but kept on swapping party members so to give everyone their moments ( and yes, some tough fights caught me without a healer)
.But once you've got the basics of the gameplay, the real "pain in the ass" moments are not more than 6 or 7.