I have played for almost 3 years now. I love the game, I love playing through it but somehow in that three years there are still quests I have never run. Below is the list and why......the purpose - maybe someone can point out my incorrect assumptions or the developers may gain a minor amount of insight into how players view the game.
1. Three Barrel Cove - before I went VIP(late 2011) I had never touched it. Now I have done the one quest on the boat - I entered the explorer area on an at level character but I was on a melee and my hire died in seconds. I left never to return - nothing is ever on the LFM and so unless I go in over level to learn the area I will likely never go in....i know i am missing out on one XP farm quest but....meh.
2. Twilight Forge - flagged for it on two characters - never see it LFM'd - don't know it and due to lack of any pugs for it I don't see the point in learning it well enough to join the one pug a week you see try to run it.
3. MA and LOB - only flagged on one, maybe two characters - none of the loot it awe inspiring and now they are rarely run so I can't even learn it.
4. TOD - only ever made boots on my monk(light monk even so I can spam stun block).....drop rate for boot mats is stupid for quests with low XP and/or other rewards and for something that is a de facto requirement to run the raid. I want to run this one, I just don't feel like being the newb.
5. Cursed Ascension - until my last few TRs I had never filled a sigil (not until the pieces started dropping everywhere) since then I have never got flagged - people grind litany but never do the wings - I had enough trouble soloing that darned beholder and Mintos that I decided to shelve it when added to the fact that it is rarely Pugged.
Basically low reward, low PUG, low fun stuff....