The End of Days Four or five years after the events of Labrynth (there seems to be some internal debate on this point), Sarah gets called back to a rapidly decaying Goblin Kingdom by Hoggle.
This one almost got a rec despite my qualms because it's really, really good for the majority of the fic. The writing is far and away better than any other serious Labrynth fic I've read, the characterizations are stunningly good (especially Hoggle and Didymus, who are both far more fleshed out than in canon and vastly entertaining characters), and it's over 100,000 words, which is in and of itself awesome. What made this harder was the fact that the issues I had with the story were (except for the last one, which is a personal squick) so minor that if there had been even one fewer of them it might've gotten that rec after all. To wit:
-Throughout the story the dialogue punctuation is wrong (she uses periods when she should be using commas). There isn't actually that much dialogue, so it's not a huge deal, but still a bit distracting.
-The story drags in places, primarily due to the excessive use of extended (and often completely unnecessary) dream sequences.
-The author occasionally uses bits of dialogue from other sources. The lifted dialogue is always referenced, so it's not plaigarism, and she doesn't do it terribly often. Unfortunately, when she's using really famous lines from really famous books, it is really distracting and consistently brought me crashing out of the fic. The most egregious instance was when Jareth and Sarah were having an argument that suddenly turned into a barely-paraphrased conversation from Pride and Prejudice. The dialogue didn't fit the story, it didn't fit the characters, and it was incredibly jarring.
-Then the author wrote a one-shot and then informed the reader that, while the one-shot was full of extraneous details she couldn't fit into the main story, you had to read the one-shot to be able to understand what was coming up in the main story. I'm sorry, but if you need to read a second extra fic to follow your story, then those details aren't extraneous, and they should absolutely have been in the main story.
If the above issues (really, all quite minor when you consider the length of the story) aren't a big deal to you, you should give this fic a try, because the characterizations and the writing are really quite good, and my last issue with the fic is one that is a very personal squick and might not be an issue for you at all.
That said: the first sex scene of the story is one in which Jareth tells Sarah that the moment she says yes to foreplay, she is giving up her right to say no to anything else (because apparently a lot of women find it really sexy when a man says, "I want you so much I'm not going to be able to stop" or "I want you so much I can't help myself". I am not one of those women; to me both of those sentences are the same as "I want you so much I have to rape you".) This is followed by some sadomasochistic stuff that I had to skim over, because WTF? Not only not my cup of tea, but something that I would have personally warned for. A mature rating (which was repeatedly warned for) does not automatically imply blood-play and sadism.
Unfortunately, that's where I had to stop reading, because I no longer had any interest in the Jareth/Sarah storyline. It's a fine line to walk between the canonical fact that Jareth is a sociopathic ass and the desire for a happy romantic ending and up to this point the author was doing a pretty good job of walking that line via emotional abuse on Jareth's part and Sarah retaining a backbone despite it all. Homicidal jealously and blood-play, on the other hand, falls on the wrong side for me, though it could easily be argued that it was very much in character for Jareth (thought I find it a bit of a stretch that accepting either of those things is at all in character for Sarah).
At any rate, a quick glance at the last page does indicate a happy ending for J/S fans. Since most of my issues with the fic are minor or very me-oriented, I'll leave it up to you to decide if you want to give it a try or not. If you opt yes, I'd love to hear your opinion of the fic; it's been a long time since I've been this torn over a story.