You will need similar lvled people to have a fun game of dungeon defenders. It's fun and challenging. Higher lvl people will just faceroll through the lower dungeons. making it not fun and giving you a "wtf is going on" factor.
Magicka is fun for new people and veterans, because there is no lvls and everyone can do the same spells. Furthermore you can trap your fellow sorcerers with 10 mobs around him and laugh at him while he screams for his life. When he dies you just ress him and blow him up/burn/freeze/electrify him to death for more shits and giggles and refuse to ress him for 5 min. When you do ress him, you know he is going to assasinate your arse the chance he gets or just freezes you in front of a few hungry packs of monsters and makes triumphed sounds while you die. All in all, you need to be a douche like me to have fun in the game
Sounds like a great game!