I have to admit that I was a bit skeptical when I first read the summary, but now that I've seen it twice, I realize how wrong I was!
The concept, the plot, the idea, I thought it was fantastic all the way up to the wonderful ending. This is by far one of the best episodes of the enitre series IMO, and I absolutely loved it!
And I especially liked how:
Spoiler Below Herriman made an official rule that had all the imaginary friends help Frankie around the house. That was something I thought was a wonderful idea and an excellent and appropriate additon to an excellent movie.