Can you… get it on… with anyone or just certain characters

I don't know if it's possible, I had Leliana joining but there was a black screen so it was not so much fun...

Maybe Morrigan must loves you for joining. Howewer you are losing nothing. Really :P

Good and fun are a bit subjective, but I can tell you what is powerful.

Crowd Control

• Crushing Prison - Both good damage and powerful cc, Crushing Prison will remove an enemy from the fight for a long time and even shatter frozen targets. It is invaluable for removing powerful casters.
• Cone of Cold - Great as a CC and for Shattering people, but I find the real power of Cone of Cold is lining up my enemies for Shock, Flame Blast, Chain Lightning (assuming you have the mana) This is just powerful dps and you don't have to worry about enemies moving. Since FB is low damage and CL is expensive, often times my combo is just CoC into Shock.
• Mind Blast - Every Mage I make has this ability. It is cheap, effective, aoe stun and I cannot imagine skipping it. It'll get you out of many pinches.
• Winter's Grasp - Though at later levels it has a low freeze chance (100-enemy level*5), and it doesn't freeze enough to shatter, it is very cheap and is useful for a large portion of the game.

AOE

• In the same mind set of CoC into Shock: Blizzard into Tempest. While Inferno is technically a better choice, I often don't have the points to go that far down the fire tree.
• Mana Clash - While technically AOE, this spell feels more like straight dps vs Casters. It is worth mentioning that this is the easiest way to get your Heavy Hitter achievement.
• Virulent Walking Bomb - More fun than useful in most situations, it still brings heavy Physical damage (but not reduced by armor). A great room clearer.
• Chain Lightning - This spell actually comes with a long cast time (2 seconds) so I like to pair it with abilities like CoC and Blizzard. Unfortunately its high cost means it's hard to work into nice combos. I do recommend it though (and really the entire lightning tree).