MMOs are games where you play combat primarily in the user interface rather than the game world.
I think this is best realised in the classic ‘standing in the fire’ error of new raiders: essentially people stand in the fire because it is an element of playing in the game world, where levelling-up has trained those players to instead play in the interface. Combat is in the cooldowns; you watch timers, health bars, debuff bars, and only when you get to raiding or the more ambitious small group dungeons do you need to start looking into the game world too, in order to step out of the fire, dodge the laser beam, jump over the furious shrew of ruin.
And what do players in WoW, LotRO and other such MMOs with LUA AddOn functionality do in response? They add UI elements that warn the player to step out of the fire. They add further UI elements to tell them who to heal, who has aggro, who to cleanse; when the boss will enrage, when the next wave of adds will come, when to run away from their team; what button to press, what direction to run, what lever to pull.
What to have for dinner.
Compare this to a game such as Super Mario where you play the game entirely within the world, and the only time you have to care about anything outside of that world is to glance briefly at your health bar. FPS games generally keep the UI to a minimum, with the player’s concentration focussed on the action in the game world, a glance at health or remaining ammo being all that’s needed, and where games such as Gears of War have experimented with removing the health bar altogether. Even RTS games –where heavy UI use is a genre feature– still have a healthy balance between using the UI and interacting with the game world, where units have to be selected and positioned within the world, and combat requires the player’s attention to be focussed on their virtual surroundings.
MMO combat, on the other hand, seems to generally draw the player out of the game world and force them into the UI, and since combat is still the genre’s de facto method for resolving all disputes and difficulties, this means that most players spend more time staring at the UI than the game world, so perhaps it’s little wonder that so many AddOns seem to add yet further UI elements for the player to focus on. I’m definitely interested to see how games such as TERA (despite it’s painfully immature sexualisation of, well just about everything really; I imagine even the boars will have up-skirt panty shots) try to use the action orientated combat to draw the player out of the UI and back into the game. Despite its many failings, Dungeons and Dragons Online did a fair job of this, and I believe it made for much more involving (albeit otherwise flawed) combat.