I've acquired DA recently and playing on Normal. seems pretty difficult to me, but a lot probably has a lot to do with what I don't do which I will get later to.
anyways, party is Alistair, Leliana, Morrigan, and my Rogue. I had problems with the undead Nightfall attack for a while until I ran my group to the dock and stayed there. most if not all mob packs have some aggro issue where you can pull off a single mob or a small group from the pack though, so I did that until they were all cleared.
then, I had problems with the Mabari pack (primarily the yellow named one) in Castle Redcliffe until I was able to get a partial pull of that group.
now, I've come across the Revenant in Castle Redcliffe and even though all the archers and melee undead were killed before the Revenant got killed, I haven't figured out how to kill him yet. all the stuns, knockdown, etc abilities seem to be resisted or have little effect and his damage his huge. I'm probably going to make everyone ranged and run around whatever character has threat on the Revenant.
now, I'm pretty sure a definite part of why the above has been difficult for me is because I haven't bothered to use traps or poisons yet, and I don't use the HP potions until a character is almost dead which results in them dieing a lot because of poor timing.
anyways, I think I should have rolled Mage. Morrigan is incredibly useful and so was that Mage during the tower climb at the beginning of the game.