In 15 years, with a proper hindsight, and after several failures or deceptions, has the genre evolved enough to keep players coming in and maintain their interest ?
1) From ICE age...
The first wanderers accross Britania, Norrath or Auberean, at that time where internet connections were costly and online games needed sturdy computers, landed on these first MMORPGs where no wiki-pages existed, no add-ons, no written strategy guides and where all the help you could have came from other players.
That early setting directly put the focus on the collective : you had to group and organize yourself with the other players, in order to do the three key aspects of the game, ICE : Immersion-Collective-Exploration
These world were huge, with no definite frontier and players had the impression to be the first explorers (which was true at that time). To distinguish themselves from retail games, these early MMOs had no real endgame : the worlds were persistent and players were encouraged to level up to, supposedly, infinity and beyond. Even first PvPs early MMOs like Dark Age of Camelot rest on Realm vs Realms and massive collective players interactions, as core gameplay.
Leveling was long, not particularly interesting, but, with shorter connection time (cost issues, especially for a young audience, not above 25 yo top), the horizon of these games seemed quite unreachable : it was the journey, not the destination.
At that time, there were raids and instances, with bosses to be killed, but all players, hardcores or "casual" (even if at that time, the term has to be relativized, compared to current casual gamers...), all of them had an event horizon as perspective. Not all content was accessible to everyone and some was even unaccessible to all... until the assassination(s) of Lord British, Ultima Online's creator Richard Garriott's character, whose "unkillability" was multiple times bypassed by players.
This unexpected event, indirectly, alongside with other massive beaten challenges on other early MMOs, had some massive consequences on the next generation of MMOs : the success and popularity of this particular event ("I was there" posts flourished on numerous videogames sites and forums, to notice the importance and impact of the event for the online gaming population at that time) was probably one of the reason of the structuralization of a real end-game for all future MMOs that came on the last decade.
After his character's assassination, Garriott, quite upset, made his character supposedly not killable and, in all the next Ultima's, players competed with ideas on how to kill this "ultimate boss".
The circle is drawn : there now was ultimate bosses in MMORPGs.
2) ...to ISS age
With the third age of MMORPGs and its massive development, mostly due to internet access democratization, end-game, since 10 years or so now, is the ultimate frontier of all MMOs.
All unknown territories have ben explored, and now, it's all about ISS : Individual Solo Storytelling.
Each player is now focused on his/her character's progression/gear/achievements. From collective exploration, we have entered in the competitive itemization period.
As there is now one defeatable last boss, there is now one parallel storytelling, duplicated for each player's character, with separate instances (SWTOR, TSW, etc.), separate phasing systems (WoW), etc.
Even games like Lord of the Ring Online, originally focused on group storytelling and immersion (players group involvement within Tolkien's storyline and social immersion through music system) have made a turn toward "soloization" and end-game.
Each expansion of the famous World of Warcraft welcomed its big bad guy (from Nefarian to Arthas and possibly Garrosh on Mist of Pandaria), and all competitors adopted the same pattern : it is the destination, not the journey.
Leveling is now a necessary unwelcomed path to follow up to the real content of the game : raids and instances, split in different difficulty levels to allow both casual and hardcore gamers to play what is now the core content of MMORPGs.
What was new, yet to discover 15 years before, is now much more mastered by players, and guilds or clans are more organized on this single goal : beat the ultimate boss in the hardest difficulty mode.
And this is not to be taken lightly by editors and developers : with the more and more "semi-professionalism" of some guilds, it's now more a race between the game devs and the players on how much time several monthes of game design work will take to be completely washed up by most dedicated players.
Compared to just several years ago, where ultimate boss of WoW's Burning Crusade, Illidan, took almost two monthes to be taken down by hardcore guilds, now it generally take only 1-2 days top (even 3 hours only if you take the last Diablo in the equation...).
The fact is simple : this battle can't be won by developers.
Continuously creating end-game content, and trying to maintain both ends of the rope (hardcore and casuals) is a losing and mostly costly battle.
3) Game with no end
If battle is lost, can the war be won over, if there is such a thing as war ?
There are currently two different ways taken by developers to address this matter : extras, or UCC.
Extras are the most common way new MMOs have handled the issue : going back to old roots and add side-content to keep players busy while or after their levelling phase or after they cleaned the end-game.
Games like Rift (with continuous invasions of the game maps, to be fought in groups, enigmas or exploration hotpoints to be discovered, enigmas, collections, etc.), or the incoming GuildWars 2 (horizon points, playful crafting system, public events), and some others, chose to keep the end-game model but simply to add side-content, that somehow help hiding the lack of regular costly endgame content to their game.
The recent Secret World, by Funcom, chose to diversify the types of quests and challenges : riddles, puzzles, enigmas, investigations, etc.
But all of them kept with the end-game as ultimate goal of their MMO.
Though, there is one MMO that tried the second way : User Created Content
The sole MMO (at my knowledge) that kept, since its launch in 2003, a constant positive curve of acquisition (more newcomers than players leaving), is also renowned for its end of end-game, Eve Online.
Also known for its very difficult off-putting prime access, Eve Online is nonetheless drawing a path for the future of MMOs : there is no end-game in Eve : appropriated ingame tools are simply given to players to let them organize themselves in this sandbow MMO. And be sure of that : players will take advantage of these tools. Internet is full of Eve's epic battles where thousands of players were involved in massive attacks on a game's planet, raids on merchants shipments or any other content THEY decide.
For developers, as explained above, the content adding race with players is a loosing battle, but giving the proper tools to players to let them write the game's own future is probably the cleverest way to address the MMO content issue.
The next step for MMORPGs should definitively follow this direction : players, after 15 years of experiencing the holy Quest-Level-Endgame trinity, are now fully mature for their own created content, provided we give them the proper tools.
But the question is : are the developers ready for it ?