It has become fashionable among the MMO literati to denigrate Trinity-based gameplay for PvE, which are games with a group composition of tank, healer, and damage dealers. I disagree with this view. I consider the Trinity-based system to be strongest group system for MMOs presented thus far, especially for the fantasy genre. Here are some thoughts on the Trinity system.
A Digression on Magic
A few years ago, according to Mark Rosewater, the Magic: the Gathering design team conducted an experiment. They stripped Magic down to its fundamentals, playing "vanilla" games with basic land, basic creatures without abilities, and basic spells. The simplest game of Magic you can think of.
They found that--far from being boring--these vanilla games were surprising fun and intricate. They didn't need the crazy complex spells to make the game interesting. The basic skeleton of Magic was more than fun enough to sustain gameplay.
They also discovered that a lot of the fun came from the interaction between attacking and blocking creatures. This did not happen as often in the Magic of that time period because cheap removal spells had made it a lot easier for players to clear a path, or evasion abilities to avoid being blocked.
Because of this experiment, Magic R&D cut back significantly on complexity in future expansions, especially on non-rare cards, made removal scarcer and creature combat more important. They moved Magic back towards its vanilla nature.
This approach has made Magic enormously successful, with current sets setting new sales records, and outselling previous sets. An outstanding achievement for a game that is approaching 20 years of age.
The lesson here is that, for a game system, the very basic game system around which everything else is built should be fun in and of itself. You should not rely on complexity to add fun.
Relevance to MMOs
The above anecdote crystallized some of my thoughts on the Trinity. In my view, the very basic Trinity gameplay is a tank tanking a monster, the damage dealers killing the monster, and the healer keeping the tank up. This very basic, very vanilla, gameplay is fun. You don't need to have all the crazy, wacky abilities. Those extra abilities add spice and interest. But I think the Trinity skeleton is strong enough to sustain itself.
You don't need things like coordinating cooldowns or excessive dancing to make Trinity games fun.
This is in sharp contrast to all the non-Trinity gameplay I've played. The vanilla skeleton of those games is usually just a zerg, with the monster switching attacks at random. I don't think the zerg is fun. It contains none of the teamwork of the Trinity, none of the sense of the group being stronger than the individual components.
The Third Role
That's not to say that the current Trinity is perfect. But the real issue with the Trinity is that one role, damage dealing, is far more popular than the other two roles. The problem is not with Trinity gameplay, the problem is constructing the Trinity in the first place.
Here's an idea: what if the third role was not damage dealing? What if it was something else, like debuffs, or interrupts, or crowd control?
This would immediately allow the game company to equalize damage across all three classes. That would mean that healers or tanks could do as much damage as the other role. This would make soloing much easier, and would make tank and healer classes more attractive. It would also mean that you could do something like requiring a group of five to need one tank, one healer, one debuffer, and two others. That would give more flexibility for group composition.
A lot of Trinity games, especially WoW, have made threat a non-issue when tanking. And yet, when we look at the vanilla Trinity gameplay, I think threat is actually important. It's a large part of the interaction between damage dealing and tanking. I think basic threat is a large part of what makes the Trinity gameplay tick.
That means that the modern move away from threat is working against the natural skeleton of the Trinity. That it might be better to re-emphasis threat, to cut away the elements that make threat excessively pointless.
To re-emphasize threat means a couple changes would have to be made. The tank losing threat cannot always be an auto-loss. The tank needs to regain threat quickly, but the group should be able to survive the mob switching targets temporarily.
In my opinion, one really sees how this works when tanking in TERA. There, the trade-off between threat and reducing damage is explicit. I think it emphasizes something that WoW tanking has lost.
Those are my thoughts on Trinity gameplay. The basic skeleton is fun and engaging. In my opinion, vanilla Trinity is far more fun than any other proposed vanilla system, especially the zerg.
However, I am not sure that the third role in the Trinity should be damage dealing. It might be better to equalize damage across all three roles, and have the third role take care of a different function.
Finally, I think the move away from threat is a mistake. Threat is an important part of vanilla Trinity gameplay. However, I think that the complexity of modern fights has masked that factor. Trinity MMOs might be better served by reducing complexity, but re-emphasizing threat.