What has always surprised me is how good they are at musical numbers. Between Bigger, Longer, and Uncut and Team America, Parker and Stone must have compiled the most hilarious two soundtracks ever. Then there's the music in the show, including "Mr. Hankey's Christmas Classics," which was essentially all music.
And yeah, the show is great on its own. I learned something almost every day. I learned that professional athletes taking steroids is like pretending to be disabled to compete in the Special Olympics. I learned that nearly every election is between a giant douche and a turd sandwich. I learned the way to get kids to stop liking something is for their parents to like it too.