Quests have been a part of Runescape since day one. When the game went public on January 4th, 2001, it only knew half a dozen quests, none of which exactly qualified as epic. Besides the errand quests Cook's Assistant and Sheep Shearer, which to this day are the quests most new players start out with, there were three quests that were mainly based on dialogue (Romeo and Juliet, Restless Ghost, Shield of Arrav), and one quest that focused on combat (Demon Slayer).
Over the next few months the world expanded, and with that expansion came more quests. It was on August 27th, 2002, that Jagex released the Plague City quest, in which players were sent inside the walls of plague-stricken West Ardougne to find Elena, a young woman who was working with victims of the plague. The quest was unique for Runescape standards, in that finishing the quest seemed to reward players with more questions than answers. Six more parts would be released over the next three years, along with several side quests. However, we haven't had a new elf-related quest since October of 2005 and there are no signs of more elf-related quests being developed.
The Elven lands have been open for years, with the outer walls of the capital city of Prifddinas continuing to taunt players to this day. We know very little of the city itself besides the fact that it's almost entirely made of crystal and that it's currently under control of the treacherous Iorwerth Clan. Beyond that, all we can do is wait and see what the dangerous elven lands hold for us.
Of course the Plague City/Elven Lands quest series is not the only one. Parts of the Avarrocka quest series (Demon Slayer, Shield of Arrav) actually predate Plague City, but they weren't classified as a single series until much later. There are several other series, such as the Mahjarrat, Sea Slug and Karamja quest series, that came about in much the same manner.
And then there are the quest series that were actually planned out as a series, and therefore have the advantage of a more structured development process. The best example of this is the Dorgeshuun quest series, which started with an investigation into an incident in the Lumbridge castle basement, and ended with a showdown with an avatar of Bandos himself. The first quest in this series was released on May 31st, 2005 and was concluded on March 17th, 2009, meaning that, on average, a new part of the six part quest was released every six months.
Many of the quest series are unfortunately still incomplete. Despite the mysterious door beyond the mind chamber, it's been nearly three years since a new section of the Elemental Workshop was opened up. The Fairy Godmother has been preparing to take back Zanaris for well over three years now. And if Forgiveness of a Chaos Dwarf would be released tomorrow, it'd still be the first chapter of the Rise of the Red Axe series released in over four years.
This appears to be a somewhat recurring theme with Jagex' quest series. It's almost as if the entire development team suffers from an odd kind of attention deficit disorder, where they throw themselves into a new storyline with rabid enthusiasm, mapping out new areas and writing witty and dramatic new dialogue files, only to completely lose interest a few months after, leaving the players with an unfinished story and unanswered questions.
The episodic storytelling looks good on paper. After all, it allows Jagex to tell a story across a longer time frame than a single quest would allow, and they can use cliffhangers to create anticipation for their future updates. Furthermore, threading old quests together in series and linking them together with new ones Jagex has been able to add some much-needed structure to the patchwork of Runescape lore. Even old quests like Shield of Arrav, which is literally as old as the game itself and which dates from a time when the entire Runescape development team could be squeezed into a small family car, was finally given its proper place within Runescape lore when newer quests delved deeper into the mysteries of the history of Varrock.
Unfortunately this simply doesn't work if quest lines are abandoned for months or years at a time. At the moment there are dozens of areas and storylines that are simply unfinished, with no new updates on the horizon. This is a shame, as for the past few years Jagex has been working incredibly hard to turn Runescape history from a patchwork of random tidbits into a solid story for players to sink their teeth into. And while they have been doing very well in creating not just a story but also highlighting that same story from different sides, it still seems that they have a very long way to go in creating a historic background that's suitably epic for the second largest MMORPG in the world.