The plot was perhaps not the most complex ever, but that's understandable and forgiveable given all the songs. I liked that it contained a number of serious notes; Pinkie being sad after everyone cheers for Cheese Sandwich, and Pinkie being even more depressed and wanting to leave Ponyville after forfeiting the Goof-Off. As fun as she is when she's her usual cheerful, bouncy self, I like it when the show shows that there's more depth to her and that she, like anypony, has feelings, too.
Then there's the songs! There were a ton, and they were all great, especially Pinkie the Party Planner. I've said it countless times, but it bears repeating: all the songs and music are a big part of the show's appeal for me. Make no mistake, it would be an outstanding show even without them, but they still add another dimension. Daniel Ingram, I love you.
Weird Al was handled very well; I was slightly apprehensive about his appearance beforehand, although I was quite certain the show'd handle it well. I'm glad to be able to say that my hope was not in vain; Cheese Sandwich stood on his own as a character, and the episode was not only obviously enjoyable even when you weren't familiar with Weird Al already, it also avoided any overt references. Those references that existed, like the grilled cheese sandwich cutie mark design (a neat little nod to Weird Al's trademark accordeon, BTW), were subtle and felt like a natural, believable part of the character and the episode's plot.
So, yeah! Good episode. What else? Apparently Pinkie's hair can be a mixture of regular poofy and depressed straight, too. Derpy made several appearances, including pigging out at the chocolate fountain (totally cute, and totally Derpy). Cheerilee as a filly was adorable, as were the others in that flashback. The RL video segments with Boneless and Gummy were bizarre; I'm not sure I liked them that much, and I hope these won't become a regular thing, although RL Gummy was funny. Rainbow's final birthaversary event wasn't a party, it was a carnival. Another Harmony Key is revealed: Boneless, Cheese Sandwich's rubber chicken. (Sans pulley, alas.)
Shave and a haircut, two bits.
Elsewhere: discussion in broniesaremagic; episode follow-up on EqD.