Increasing coop difficulty?

Hi,

Some friends and I are playing this game on LAN in the weekends and to some extent enjoying it (most are ex-wow's). Our only problem with this game is that it's too damn easy. We're tried to tune everything to the max, which only effect is that our tank(s) need to take the damage in order to survive. What we feel is missing, which wow handles better, is the time required to kill someone. It kinda feels like being Sir Lancelot in Monty Python and the Holy Grail.

So my question, are the any way to make the fights last a bit longer, without breaking the game?