These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Eakins Hard Reset
Angst? What Angst?: Averted. While Twilight for most of the story takes her many deaths in stride, she delivers a scathing rant to Celestia about how horrible dying is when it's suggested that her friends died well, and winds up committing suicide when Luna gets killed. After breaking the loop it's made clear that she's suffered immense psychological trauma from repeatedly dying, the stress of being trapped in a time loop, and seeing her friends die over and over. She ends up experiencing nightmares, flashbacks, becomes terrified of making a bad choice with no way to correct it, pushes her friends away and starts turning into a recluse.
Crazy Awesome: Pinkie's suggestion for what will happen if both copies of the Element of Magic were ever to touch
The entire time loop; being forced to relive an invasion over and over, dying painfully in the process and repeatedly watching those you care about getting slaughtered.
While it's implied that Twilight's death immediately resets the loop, one can only imagine how terrible it would be for Celestia in the loop where Twilight commits suicide, if the loop doesn't immediately restart. Right after having lost her sister, she leaves for a while only to find out her beloved student has now killed herself.
A Stitch In Time demonstrates that several timelimes, including that particular loop, do not immediately cease to exist just because Twilight dies. Main timeline Twilight has undergone somewhere over a hundred loops, while Queen Twilight Sparkle underwent so many more than that she considers a hundred loops meaningless. Now there's a bit of horror for you: thousands of worlds consumed, irreversibly, by a wall of bright light.
Squick: The Reign of Queen Twilight Sparkle is tagged with a warning that gruesome things happen during it, and it's warranted