The first three are understandably choppy as it's developing the characters. They find their mark by 4, but really hit hard in 5. The last couple had some great breaking with the expected style and format. While the finale fell flat, it's largely due to the penultimate episode being a clip show... followed by a partial clip show.

I can't remember offhand exactly which episodes are from which season, but to my memory the later seasons were a little less grounded; more goofy stuff. Not bad, just different.