Very well written, save for a few not-too noticeable flaws.
First, the voices were almost all spot-on, notably Phil Hartman's characters (of course), though the impressions of Wiggum, Fat Tony, Moe, and other minor characters weren't that accurate.
The concept of Troy McClure and Lionel Hutz sharing a story together is interesting, but never explored in the actual show, mainly due to Phil Hartman's murder and the characters' subsequent retirement. Despite that, you definitely made it work. Some might say you belong on the actual Simpsons writing team, but in reality, you're probably too good for them.
Maybe they borrowed a bit too much from the "A Fish Called Selma", especially when the dolphin is revealed to be able to talk/sing.
Overall, a brilliant Simpsons parody that harkens back to its golden years.