I remember that story... for those of you who didn't know, Alan Moore used one of the issues of Swamp Thing to do an homage to Pogo, where aliens in spacesuits, who were thinly disguised versions of the main Pogo cast, briefly visited Earth.
Quite frankly, unlike just about everyone else on the planet, I didn't like it much. Yeah, it was supposed to be an homage to a great comic, but the entire thing wanted so badly to capture the "Walt Kelly" tone and feel and failed spectacularly... mostly because Alan Moore seems to have missed that while Pogo's satire was often biting and sometimes downright gloomy, it was never depressing. Which Moore's story most definitely was.
(I felt the same about the Wile E. Coyote homage in Grant Morrison's Animal Man, by the way -- the story was just too depressing for me to really enjoy it.)