Party of one was landmark in my opinion.
Why? I found it a deeper look at the consequences of isolation and social interactions.
What gets to me in the episode is that eventually during pinkie pies semi psychological break, the inanimate objects she's making. Voices for, from her perspective, begin to talk on their own.
This is evident of how close she becomes to having a complete break. Had Dash not wondered in, I'm pretty sure wed have seen a full blown episode.
A pity in a few ways but still, very few people I watch it with get that element. They say I'm reading too far into it.
It shows me that under all the happy and friendships and hugging and songs, there are serious problems each character honestly has.
Remember, the brighter the picture, the darker the negative