Perhaps the first episode that works without being funny.
The Cutie Mark Chronicles is not particularly funny. There's a few laughs here and there, but the episode is largely free of anything recognizable as a joke. Despite that, it's one of the season's very best.
This comes down largely to the story itself. This episode boasts some of the strongest world building in the first season, being built from pieces of exposition. Learning about the pasts of these ponies we've come to know is undeniably intriguing, and each of these stories contains the feeling that the main six are some very special ponies. Aside from that explicitly stated, there's a common thread of uniqueness in each pony's story.
The wonderful coincidence of these ponies coming together through Dash's sonic rainboom is itself quite heartwarming. It's a show about friendship, but this episode hints at so much more to it. This special link between them feels like the culmination of their growing friendship over the course of the season. But even outside of the show, this reflects metaphorically on real friendship, as is shown in the lesson.
Still, it culminates in a lesson that is a bit too wrapped up in metaphor. This element is in particular a bit of an issue with the episode, as it shows the third time this season that the actual lesson has been bungled. Sure, what it's saying is mostly fine, but the use of metaphorical elements that are shown physically in this very episode gives the impression of a lesson that only works with the reality of the show.
The other issue I had with the episode was that Applejack's backstory, as cute as it is, seemed less special than those of the others. I felt from this that Applejack was getting kinda neglected. She's not shown in a lesser light than any of her friends, but ultimately she has less special attributes, meaning it's harder to put a finger on what makes her stand out. Still, I think there is something special about her-I'm just not entirely sure what it is.
Of course, there's still a few jokes here and there, and every single one is a hit. However, most of the appeal is from the cuteness or coolness of the stories, and the heartwarming nature of the ending. There's also a bit more cerebral appeal to this episode than the ones previous to it, as is seen in the ties between the characters and the way they stand out.
This could have been a season finale for how much it wraps up, but there's still the Gala to attend to. There's a few episodes until then, but this is the home stretch of S1, and definitely a turning point towards smarter, deeper writing.