Blizzard is known for being super critical of itself, from my vantage point I don't see anyone beat themselves up more over game decisions than those connected with the design and development of Warcraft. Yes, WoW trolls are a ruthless bunch, but so is the responsibility to millions of well-meaning players. In asking this question, which I'm sure others have contemplated before, we can get at the very root of why this game has the particular unique nature of having so many lovers and haters all at once.
For me, the greatest mistake and triumph are closely tied together. The mistake is gear progression, and the triumph is the random dungeon group finder.
Let's examine both and how they lead to much of what we love, and hate, about this game.
What Not to Wear
This might be a bit controversial, however at the base I feel it's true: WoW's biggest mistake is how it fundamentally handles gear progression. As we've seen lately from Ghostcrawler, a de-emphasis on the marginal upgrades of gear is theoretically a good thing, and in that discussion it leads to the simple fact that there are many disparate views of how gear should be handled.
Grouping people into large camps, some groups see gear progression as a necessary reflection of skill and accomplishment in the game, while others see it as a necessary evil to their (and their group's) enjoyment of the end game content. Because at its heart WoW is about the freedom of choice (or the freedom of illusionary choice), we get a situation where the game must necessarily support both styles of play. One where gear is taken to the extreme and marginal gains are treated as necessary, and the other where gear becomes a low baseline for progression.
This can be seen more clearly in the raiding tiers established in the game today: LFR (gear has a low baseline for entry), normal (the baseline is raised somewhat), and heroic (living on the margin of gear improvements becomes necessary). Now this isn't to say that there are not other factors involved here, there certainly are in skill and time commitment, but at a fundamental level the game, and its resulting systems, is about gear and the progression there in; and thus so are the raid tiers.
This becomes WoW's greatest mistake due to the way the players react to the gearing. Being the best is hard wired into many of us, and we look at LFR after completing it and see more challenges to face in normal and heroic. It's only human nature to want to do more, and WoW is a beautiful example of the psychological pull to never stop achieving, even if it's for, literally, meaningless Achievement Points. It is in this frustration at never being able to say "I have the best gear" for very long and instead having to say "I need to keep playing 20 hours a week in order to try to get the best gear" that WoW fails.
Of course this could be seen as the reason for its success too (and thus why this is a deep and complex argument), however in my experience the number one reason people stop playing is because they don't find the constant gear grind fun anymore. While this is not saying that people are to blame for this system (after all, these concepts have been present before computerized RPGs where even a thing), it is still a problem.
The solution? It's time for gear as we know it to be removed from the game. You can check my twitter feed around April 22 for more on this, or just wait until I publish the article on Monday.
Clark Griswold's Family Vacation
If the gearing progression is WoW's greatest mistake, than the greatest triumph is the ying to its yang: the random looking for group finder. Dungeon running back in the day used to be a thing you got together once a week for around the dinner table with friends. You'd pull out your character sheets, sharpen your pencils, and parade around a cave fighting off dark elves and beholders.
Fast forward 25 years and you could wait around for an hour to find the right group comp to run LBRS or for your guild's tank to get on. It was a lot better than a once a week activity, but it still wasn't something that could just happen for 45 minutes and be done with. And heaven forbid you had to replace a group member ... that'd require a trip back to the city and another lengthy wait.
Then along came the random dungeon group finder, and you were no longer bound by anything. You were free to roam the open road of WoW's dungeons. You'd queue up, wait around for a few minutes for the group to form, and then go off stomping enemies left and right. If someone left the group you'd just have to queue up again, go refill your coffee, and when you came back you'd be nearly set.
That's some crazy evolution, perhaps some of the greatest game system design in the history of gaming. Groups went from taking a week to form to taking 15 minutes. Dungeons went from a special thing to something you did every day before bed. They became routine, expected, and endlessly fun. This is where World of Warcraft's greatest triumph lies. Whereas Apple has personalized the phone and the computer, Blizzard has personalized Dungeons & Dragons; and it has succeeded in business in like regards.
I'm interested to hear what you all think, however I again reiterate the start of this article where I ask for this not to be trolling. Give this some thought -- it's easy to jump out and say Cataclysm was WoW's greatest mistake, but that's lumping a lot of good things in with the bad, LFR is on the top of my list in WoW's greatest triumph. If I get the opportunity to speak with the designers on the record at BlizzCon this year, I'm likely to just ask this one question to them. I think it'd provide a lot of insight into what WoW is and where it's headed -- and as a community, let's come together and start talking about that through its history.