Old Shame: Trey and Matt feel this way about the show's first three seasons, as noted in an interview for Entertainment Weekly, "it's just embarrassing to watch." In one of the commentaries on the season 3 DVDs, the duo mentioned that they considered season 2 to be particularly bad, which is why there are no commentaries.
Trey is an admitted Japanophile (and majored in Japanese studies in college). The South Park episode "Trapper Keeper" directly parodies Tetsuo's meltdown in AKIRA, the Japanese spoken in "Chinpokomon" is accurate, and "Good Times With Weapons" is an Affectionate Parody of shonenanime like Fist of the North Star. He went a step further and married a Japanese woman (though they have since divorced).
The show is also full of references to Star Wars and Star Trek, and both Parker and Stone are avid video gamers (hence the show's unusually detailed and accurate references to video games and game consoles).
Apparently, Parker and Stone were at one point asked to write the sequel to Dumb and Dumber.
They were also set to write a film called "My All-American" at one point, as well as one titled "Giant Monsters Attack Japan!". Both projects fell through, as they remembered how burnt out they got on Team America, as well as wanting to focus more on South Park and (eventually) The Book of Mormon.