I've got one word for this episode, just one word: Epic.
There was definitely no shortage of funny moments here. My favorite moment was when Cheese Sandwich started singing "Smile, smile, smile" and Pinkie goes "Hey! That's my song!" (clearly a reference to the fact that Weird Al does song parodies)
Speaking of songs, I anticipated there would be a lot in this episode, so I had decided to keep count as I watched, and came up with a total of seven songs (surpassing even Magical Mystery Cure, the season 3 finale). I can't even remember half of them, but they certainly helped to move the episode along.
I also liked seeing that flashback that not only explained Cheese Sandwich's backstory, but also showed him, Pinkie Pie, and other background characters as foals. I would not be surprised to see fanart of this soon afterward.
As I had expected, Pinkie Pie had her "rainbow moment" in this episode, and received a gift from Cheese Sandwich. What was this gift? A rubber chicken. I had not anticipated that, but in hindsight, I probably should have.
A good episode indeed, and I can easily see this one becoming a fan favorite.