The Simpsons - Season Four on DVD

I finally received my copy of season four of The Simpsons on DVD, and I've been playing it in a spare window on the computer all night.
Brilliance, just sheer brilliance. The show is still decent, but season four is the show at the peak of its powers. Phil Hartman was still alive, and the sheer density of clever pop culture references is staggering. If you wanted to own only one season of the Simpsons on DVD (poor you), then this is your box set.
Now that Seattle is working on finishing its monorail, the episode "Marge vs. the Monorail" is satire that strikes particularly close to home. I'm crying. The British may be the masters of comedy, but The Simpsons may just be the epitome of American humor, a balance of optimism and indiscriminate skewering chock full of references that draw from culture both high and pop (America has no highbrow or lowbrow culture, just a democratic soup).
Speaking of The Simpsons, is there any badge of cultural distinction greater than appearing as a guest star in an episode?