I have a 5 x Mages team, currently level 63, and they are a lot of fun to play. Or lets say, a great way to relax after a day at work. They feel a bit like an old school Beat'em Up arcade game in the way their game-play is over-simplistic : 3 buttons, and everything else dies.

They are specialised in Arcane, so a standard game sequence would be : bubble-up, run, grab mobs, and then Arcane Explosion until everything is dead.
On single targets and when they are attacked by horde, arcane missiles x 5 and arcane barrage x 5 make wonders.

Also, 5 identical gnomes running around tend to turn people insane, which is also fun.

Of course I don't run instances with that group, not possible unless they badly over-level the place.
I already ran them by three together with tank and healer from other groups : Grab a pack of elite mobs with the paladin, and then run in with the rest of the group. 3 x Arcane explosions + Priest's Holy Explosion on mobs that are aggro'ed by a plate wearer ... That was fun.