In the summer of 1999 Trey Parker and Matt Stone released "South Park: Bigger, Longer, and Uncut," which was easily the best musical of the 90's. In Christmas 1999 they solidified their reputations as musical masterminds with this Christmas special.
How else can I put it? The songs are just too good! They're fun, imaginative, and never ever EVER boring. Never ever. Plot? What plot? There's Christmas songs, and the South Park characters are singing them... to musics and lyrics arranged by Matt and Trey! What more could you possibly want? I'm serious, watch this episode, right now! And rewatch it every Christmas. After "The Woodland Critter Christmas" (Season 8), this is South Park's best holiday-themed episode.