Better than expected
There is a certain bias, and not without reason, against self-insert fan fictions. It's little wonder, as most tend to be garbage created solely for the purpose of pretending you're wooing the bishie dude of your dreams, or making out with some tsundere chick. On the other hand, there are very, very good self-insert fictions that make you see the genre differently. Stories like "Mass Vexations," or "Sleeping With The Girls," which are phenomenally good stories that delve deeper into the underlying characterizations of the story and make you think. While not as good as those two stories, "Stuck," makes a darn good attempt at being so. The characters are believable, the interactions they have with one another are plausible, and there is a distinct lack of Mary Sues anywhere in this story. The closest to sue-dom the SI gets is that the ponies seem to like him almost immediately, but one must remember that this is the same universe that was able to throw a "Welcome to Ponyville," party to Twilight with several dozen attendees within minutes of her arrival to the town, so their standards of liking him quickly are different than ours. This isn't one of those really deep fics, or super awesome ones, but it is a fun one. I give it a four out of five stars.