It used to be the case that the serious gamers played any of a dozen different tabletop RPG systems — Dungeons & Dragons and its knock-offs, Champions, Cyberpunk 2020, Shadowrun etc. Serious players would spend anywhere from four to twelve hours at a time, maybe several times a week. But for all that, you didn't really get a lot done in one of those marathon gaming sessions. Sometimes, you might manage to get from one town to the next, or maybe only part way there, or you might maybe clear a couple of rooms of the current adventure "dungeon" that you'd been working on for the last couple of months. But you'd seldom accomplish more.
Quite simply, the mechanics got in the way. Playing AD&D or Champions was time-consuming. All the rolling of dice, calculations, looking up tables, and the gamemaster's decision-making on how to resolve events — with one player at a time, most of the time, while everyone else sat and twiddled their thumbs — unavoidably consumed a lot of time. Players spent most of their time just waiting for their turn to try to do something while other players' turns were resolved. With more than about four or five players, it rapidly became completely unmanageable.
Still, it was the best we had, at the time. But sometimes just plain waiting for the mechanics could get pretty boring. We did everything we could to speed it up. I and a friend who played Star Fleet Battles wrote a program on a HP handheld "computer" (by modern standards, scarcely more than a programmable desktop calculator with a thermal printer) to automatically generate damage results because, even with the very basic capabilities available on such a primitive machine, it still sped up damage resolution by a factor of about ten times. In the group I played AD&D with, we totally redesigned the combat and magic system to almost entirely eliminate page-flipping and table lookups — there was only one chart for hit resolution, and unlike the original highly non-linear AD&D hit tables, the math was simple and predictable enough that you could do it in your head in seconds, needing to know only your class base hit probability, your total bonuses, and your target's armor class. But even with every possible speedup, the mechanics still took way too much time.
Early computer video games didn't have a lot of depth. Eventually, though, things like Neverwinter Nights came along, basically modelling AD&D or similar games on a computer and letting the computer handle the mechanics.
Well ... most of the mechanics. But here's where things took a wrong turn, which I'll come back to in a moment.
Now, there are any number of online MMORPGs. Everquest was probably the first really successful one, World of Warcraft is the biggest and arguably the most successful, but there's also (for example) Lord of the Rings Online and Dungeons & Dragons Online, both from Turbine, as well as City of Heroes, Final Fantasy, Runescape, Wizard 101, Hogwarts Online and a host of others. They have varying degrees of depth, and varying complexities of mechanics. But the crucial thing that most of them have in common is this:
The mechanics are transparent. The game handles essentially ALL of the runtime grunt-work for you. You have freedom to decide what actions you're going to take, of those available to you, but you don't have to keep track of which actions are available; the game does that for you automatically, and keeps you up-to-date visually about the state of your ability cooldowns. You are freed to just PLAY.
But notice that I said "most of them". There are a few games among the pack that are dysfunctional in varying ways. Dungeons & Dragons Online is one of these, and I'm going to use it here as my main example. Its particular dysfunction is that it preserves all of the complexity of the original AD&D rules, and applies them automatically, but it applies them in a curious mix of things that you need to know which it doesn't inform you about — it expects you to just know them — and things that you don't need to know about, but which it bothers you with anyway.
For example, there are cryptic rules about when bonuses on different items stack and when they don't, for example, and the game won't tell you. You have to either already know the rules, or figure out what's happening and why with very little help from the game. (The general rule can be summarized as, "Ability bonuses don't stack, except when they do." The game never explains this.) It will teach you the bare minimum interface mechanics you need to know to play the game, but beyond that, it simply expects that you know the more complex and less obvious mechanics from playing tabletop AD&D, and current AD&D at that. This does not in any way add to the game experience. It's just opaque complexity that the player has to keep track of.
And then there's saving throws. Certain events — being possibly poisoned, say — trigger a saving throw in Dungeons & Dragons Online, just as in tabletop AD&D. The online version models this, and puts up an onscreen reminder that you have a pending save and a countdown in seconds to the future moment at which it's going to actually be resolved, and actually goes so far as to "roll" a little animated icon of a D20 in the corner of your screen ... which is completely beyond your control. You cannot affect the roll in any way. The game is bothering you to let you know about an underlying game mechanic that is completely non-interactive and outside your control, just to bother you about a background game mechanic that you can't even do anything about. (And in any case, when I played tabletop AD&D, saving rolls happened immediately to determine whether you triggered or evaded something. What's with this 20- to 40-second delay to figure out whether something already happened to you or not?)
What's going on here is, to a large extent, misplaced nostalgia. The fact is that many of the underlying mechanisms of AD&D (for example) were devised for a tabletop game in which the mechanics are done by humans with dice and pencils, and they do not translate well to a game model in which all the mechanics are managed by a computer. Dungeons & Dragons Online is not alone in this; I've seen a number of games over the years that fall into this trap. Wizard 101 is another game that falls into this general class of error; it's largely an MMORPG wrapper around the underlying game mechanics of Magic: The Gathering with the serial numbers filed off, and the massively immersion-breaking Magic-based mechanics are like a whole herd of elephants in the middle of the living-room.
Mechanics are, in fact, at the core of the underlying problem with the various games that I have branded as "dysfunctional". There is a single basic misconception here: the idea that preservation of the mechanics is more important than the gameplay. The designers of these games have fallen into a conceptual error of thinking that it is the mechanics that are important. And that's just not true. Actually PLAYING any of these games has NEVER been about — or for the sake of — the mechanics. The mechanics were a necessary evil to make the game work; but the gameplay was about the play. The mechanics were simply required in order to make the play possible, and you dealt with them because there wasn't a better way.
In this age of computer-managed MMORPGs, yes, players still need to know and understand the mechanics of the game — as far as how their character class and their abilities work, how to best optimize and tailor their abilities, how to select equipment to best optimize their gear bonuses to maximize the balance of talents and abilities they have chosen to emphasize and rely on in their character build. Game mechanics still affect all of those choices, and a well-designed game gives you immediate feedback on, for example, gear choices so that you can see exactly how swapping one specified item for another will change your stats or bonuses, without having to know a cryptic set of complex rules that the game doesn't explicitly tell you anywhere. But there is no reason any longer for management of those mechanics to get in the way of the actual gameplay. That's the game's job — to free up the player to just play.
As alluded to above, though, there are a number of games whose designers have made the conceptual error or instead prioritizing preservation of the game mechanics, sometimes through misplaced nostalgia, sometimes through simple failure of imagination or design. In quite a few of these games, the mechanics are not only unnecessarily obtrusive in ways that break immersion in the game, they actively interfere with and obstruct the actual gameplay.
And when the mechanics of your game, for no good and necessary reason, obstruct the play of your game and force the player to break his or her immersion in the game to deal with mere mechanics, then you have failed at game design. The game mechanics are, quite simply, necessary underlying structure for the workings of the game; and that is all they are. They are not the purpose of the game. The gameplay is the purpose of the game.