Diary of a Ruler, by Lamia (about 2800 words (10%) read)
Zero-ish spoiler summary: Excerpts from Celestia's diary, containing her musings about life, immortality, and all sorts of other stuff.
A few thoughts: To put it succinctly, Celestia here sounds like an angsty teenager. It's full of unselfconcious dismissal of everyone around her ("I wonder about my complex thought processes. I look at the average individual; they have little to no worries. One wakes in their bed and make plans a day at a time"), and short on actual depth. Even if one subscribes to the "regular ponies are ants compared to Celestia" school of characterization, you'd think she'd approach the subject of her subjects from a less myopically self-important perspective.
Recommendation: This is definitely one to avoid for readers who dislike the "immortal angst" genre. Beyond that, it's a well-written look at a self-absorbed but un-self-aware individual; if you can reconcile that characterization with Celestia, this might be worth a look.
Death By Dragon, by Compendium of Steve (about 25,000 words (20%) read)
Zero-ish spoiler summary: In a dark alternate Equestria where Twilight, upon becoming princess, made books her first, second, and only priority, Spike is tasked with tracking down delinquents who fail to return books to the library in time, and dealing with them... with extreme prejudice.
A few thoughts: This kind of story (grimdark AU) isn't usually my cup of tea, but I actually enjoyed it at first; there's a bleak humor pervading the story, a lot is made of the contrast between the murder-happy plot and the Equestrian setting, and Spike's noir-style makes for a nice narrative voice. But there's a lot of fourth-wall stuff here, and I got well and truly sick of it by chapter four (where, among other things, Spike tells the reader that if they've got any questions about a certain event, they should get someone in the comments to explain because he can't be bothered). There are also some noticeable writing issues: missing/misused words and the like.
Recommendation: If you're interested in a dark comedy, this one has a lot going for it, and the way it plays with and exaggerates its characters and toys with the tone. If you're sensitive to writing issues or immersion-breaking material in general, though, I wouldn't suggest this.
Monsters, by Sharpe Quill (about 17,000 words (20%) read)
Zero-ish spoiler summary: The quiet town of Dock is rocked by a warehouse fire--and a pair of deaths--and Captain of the Guard Belle is going to find out exactly what happened.
A few thoughts: The story's short description gives us this tantalizing question: "When Twilight returned from Tartarus, she claimed no monsters had escaped. What if she was wrong?" Unfortunately, I never got to that part; while there's some nice setting-building in the author's take on Dock, the characters which populate the story are a letdown. Or rather, the narrative emphasis on physical features, coloration, and other ephemerals at the expense of actual characterization, coupled with Belle's tendency to over-narrate her opinions on everything anypony does, make the story feel very slow and ploddy.
Recommendation: As I said, I never actually got to the "out of Tartarus" stuff, so I can't really comment on the adventure aspects of this adventure-tagged story. In light of that, it might be worth considering for fans of the premise, but only those not put off by very delayed gratification (at least 17,000 words, anyway) and general slow pacing.