My problem with the "freedom" the current system allows is it allows thing like this to happen:

http://www.youtube.com/watch?v=sDk94b3oZbs
http://www.youtube.com/watch?v=KazOD98mqr4

Yeah that's right a THM soloing NM's that are designed for 15 people to fight, now I don't know about you but I consider that to be over powered. I am sure the player has a lot of skill to be able to pull it off I don't doubt that for a second but this is the kind of stuff that will be common place with the current system and this is only the beginning. I already see people trying to copy his setup and as more and more over powered setup's are discovered then you will have less and less freedom with making your "unique" class as people will start expecting you to have this setup if you play that class, especially for endgame.

This is the problem when roles aren't defined and restrictions aren't put in place.