I'm posting this again because I may have accidentally made a new comment instead of replying to you. I'm still working out the kbin kinks...
I haven't played Magicka so I can't compare (although reading the comments I feel like I have to play it now) but for me, what makes DD great is its smooth combat system. It's real-time action with varying casting times, so you need to be strategic about how you cast spells and when. Your character can switch classes pretty much whenever you want and you gain access to different spells the more you play certain classes. I could go on, but the last thing I'll say is that I've never played a better version of "magic Archer" in video games.
One massive downside to the game is its story; It's pretty much non-existent. But if you like awesome combat and party management it's one of the coolest games out there. And I haven't even mentioned the pawn system yet lol