The one mage fight I always remember was a sidequest one. You're contracted to kill 4 Maleficar in a forest. Except, you have to talk to them before you kill them, meaning your party starts the fight bunched up. If those mages get off a Cone of Cold before you get off your spell, you're dead.
I think the most hellish fights were against the Revenants. Rather than the complete jokes in DA2 (or the Aviergan Scrolls missions which are just trash mobs, lieutenants and the big boss guys) those guys were just a pain to fight. I remember going in to the Circle Tower as the first part of the game to complete with me (S&S warrior), Alistair, Leliana and Wynne, and Leliana would always drop first from Double Strike and then i'd always lose Wynne if I didn't keep her out of range. Then it was just a case of making sure I have enough mana and lyrium potions for healing spells and poultices for my character and Alistair to heal themselves.
As much as I enjoy DA2, the combat in it is just cheap. The balancing sucks, as it's simply low HP and massive damage output (player) countered by low damage output and massive HP (AI). Hell they don't even use the same spells as you (enemy mages: AOE spell, bolt, teleport, forcefield / enemy rogues: deadly backstab, nature damage inflicting backstab, stealth and backflip stealth [which by the way knocks you over because the talent is actually
directed on to one of your characters which is what I found out by testing out the AI talents, therefore making it impossible to deflect] / enemy commanders: buff, stun, AOE) which just makes it feel false. I just hate having to fight huge mobs for absolutely no reason whereas in DA:O it really felt like there was some semblance of a reason behind each battle (the undead corpses in Redcliffe or the Circle Tower are obviously no friend of yours, but they're not overused, the gangs in Denerim will obviously target you, more so when you kill some of their buddies in one of the other alleys, or getting caught stealing in Denerim causes an absolute

-ton of city guards to go after you, among others). That was probably made easier as the Darkspawn were the main enemy, but even against humanoids I felt each battle made perfect sense rather than the "oh look, I bumped in to 30 thugs who'll just hunt me down even though I did nothing", which is made worse since i've got the no gibbing and no disappearing body mods installed which makes it impossible to suspend my sheer disbelief when i've turned a Lowtown street in to a complete graveyard full of corpses within 20 seconds or so.
I know i'm rambling, but battles felt so much more convincing when you and the enemy were on equal footing since you had
exactly the same choice of spells (though obviously the enemy would have had a few less, or creatures/demons had a different set), animations and similar HP levels (Lieutenants having slightly more and bosses having a bit more from that) where rather than giving bosses tens of thousands of HP and high elemental resistances/immunities, despite all of those being increased they focused more on increasing their actual damage output; the sheer hell i've had trying to slay Flemeth because of her deadly attacks made the fight more fun rather than the high dragon at the bone pit which involves whacking it with a warrior to draw attention and three ranged characters to hit it from a distance, equipping your characters with fire resistance runes and at certain phases just dealing with the huge trash mobs of dragons and dragonlings which just spawn out of thin air (GRAAAGHHH I HATE THAT) and then going back to whacking the high dragon with everything you've got (making it brittle then using a fully upgraded assassinate does nicely too if you're a dual-wielding rogue).
You would have thought too considering all the money the player ends up getting, like all the other guys you meet in the game you'd at least be able to hire a bit of muscle to protect you and deal with the annoying mobs when travelling during Kirkwall nights.
Ehhh ... Dragon Age 2 was a game with so much untapped potential because of its short development cycle, and as much as I detest the concept of it, Kirkwall could have made for a good setting in a multiplayer game where players can become mages or templars (perhaps travelling under the gallows to root out the mage underground, or as a mage to bust friends out of the gallows), or maybe even part of the Carta, Coterie, Kirkwall Guard, mercenaries or smugglers trying to achieve their own ends to get a monopoly on the trade going through Kirkwall, or perhaps to desperately maintain order in the city (guard). Then again, I do love Bioware's stories so maybe they should just stick to single-player.