South Park always manages to reward slightly critical viewers like myself.
South Park has business-sense. It's creators and contributors are adept at "playing the game," as is the case with any successful pop culture entertainment enterprise.
There's at least a couple every season that are comedy classics.
Last season, "Cartoon Wars" (1 and 2...takes some playful shots at The Simpsons hehe(although The Simpsons was first to successfully parody other successful animated satires)...is discussed in the interview Bunbury posted) was good and I loved the return of towelie in "A Million Little Fibers."
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Two Days Before the Day After Tomorrow" is funny, but it's also convoluted.
In season 7, "Woodland Critter Christmas" finally delivered delightfulness.
Although, their "Something Wal(l)-Mart This Way Comes"from the same season is a perfect example of (by this particular episode's end) a short-sighted, smug, Republican agenda.
Only a few seasons ago, SP busted out "Raisins" (good for the "goth" sub-plot), "Cancelled", "Red Sleigh Down", "The Return of The Fellowship of the Ring to the Two Towers", "Towelie", and the glorious "All About Mormons."