There have been games that skip the basic trinity such as asherons call and guild wars 2. In these types of games you pretty much fend for yourself as everyone is dps with self heals or aggro skills. Personally I think these types of games are not as much fun as those who follow the basic formula.
Reason being the basic MMO player needs certain constraints/roles to be able to function in a group setting. A good healer/tank combo is all you need for a group if you have those two just grab random dps to fill the remaining slots and you can run basic instances without much worry.
Gw2's mechanic just doesn't work IMO.
What does everyone else think?