We all know what the conventional roles are in a MMO - at least, a fantasy genre one. Their most basic grouping is the 'Holy Trinity' of tank, healer and damage dealer. Getting slightly more complex, we can easily identify the 'rogue' sort of character, who tends to be about stealth, backstabbing and burst damage, and the 'artillery' character who deals damage from afar but is weak up close. The concepts are pretty fundamental by now. We all know what we mean if we talk of a 'mage type character', for example. The fundamentals' origin can be traced all the way back to early D&D: fighter, cleric, wizard, thief.
Many, but by no means all, games will include some variant on these. City of Villains was one game that tried to break the mould of conventional roles. Brutes were good at tanking damage, but also built up Fury that enabled them to deal good damage back. Masterminds, a pet class, were in fact intended as the tank substitute. Even so, the basic roles still surface: people look for stone brutes to act as tanks, and some corruptors embrace the 'healer' role, ignoring their attack powers in favor of healing ability.
Just how inescapable are these roles? Is it worth a game designer's time to try to think beyond the basics, or are the conventional roles a necessary part of the way MMOs work? Do you prefer games that roll with these concepts, or games that work around them?