Life in the small town of Springfield, USA goes on as always, until outsiders begin to notice that the entire area is an environmental nightmare. As always, little Lisa Simpson petitions to overturn the continuous pollution and general disregard for nature - and for a while, the community begins cleaning up its act. Leave it to Homer Simpson to screw the whole thing up; his adoration for a new pet pig results in the quarantine of the entire town. EPA officials get presidential approval to seal Springfield in a giant dome, and the townsfolk turn on each other in panic and desperation.
When it is discovered that it is Homer who has sealed Springfield's fate, he and his family are cornered by the angry townies. They make a last minute escape from both the lynch mob and the dome, and head north to a fresh start in Alaska. It becomes apparent that Springfield is to be destroyed completely, but Homer refuses to help save the very town that he has doomed. Marge, Bart, Lisa and little Maggie leave him and return to Springfield - signaling an end for both the town and the Simpson family unit.
All of the fantastic and funny characters from the TV show are present and accounted for, and there are some hilarious bits featuring Ned Flanders, bartender Moe, the evil Mr. Burns, Chief Wiggum and others. The writing is sharp and satirical, and the story pokes more than a little fun at the current Al Gore/global warming fracas. Composer extraordinaire Danny Elfman's classic theme-song is transformed into an amazing film score (including a recurring musical cue borrowed from another 2007 summer blockbuster). The show's typically wonderful animation is even further enhanced for the widescreen presentation. I must admit I have missed many of the show's more recent episodes, but I am undeniably a Simpsons fan. And this is one great episode - one that ensures that the series (television and film) will continue on for quite some time.