You knew this was coming, right?
South Park: Bigger, Longer, & Uncut (1999)
We'll talk after the trailers.
I'm not going to explain or apologize for my love of musicals. If you can't handle the singing and dancing, stop reading now.
A lot of people aren't into musicals. (Our friend Bryan, for one, despite being a Disney superfan. Ironic.) Note that in the South Park movie trailer above, the only hint of the actual film being a musical is the Big Gay Al bit. Of course, if you've seen the TV series, you'll know that musical numbers are a frequent occurrence; even the original short included a couple of songs.
Maybe Paramount thought people who hadn't seen the TV show would be less likely to want to see an animated musical than a for-mature-audiences cartoon. In any case, creators Trey Parker and Matt Stone do a brilliant job of subverting both genres, which is not surprising considering their early film work Cannibal: The Musical! and their recent Broadway triumph The Book of Mormon. Not to mention eighteen seasons (and counting) of South Park episodes.
(Speaking of which, the documentary 6 Days to Air: The Making of South Park is a fascinating look at TV production. You can also check out Showrunners: The Art of Running a TV Show for a broader overview of the industry.)
The preview for Frozen touts its music but does NOT showcase "Let It Go," perhaps because Disney never expected that particular song to be such a runaway hit. Sure, it's designed to be a show-stopper, but it is by no means the best number in the book: it's basically a rehash of "Defying Gravity," Idina Menzel's act one closer from Wicked, in terms of emotional beats; and the lyrics are, let's be honest, not the best. (She literally says "the past is in the past" at one point, you guys. LITERALLY.)
That song sells—boy, does it sell—but it's in the recording, not on the page. (I still say "Love is an Open Door" should have gotten the Oscar nomination instead.) And my favorite lyric of the whole show, "like a girl who's bad at metaphors," actually comes from a song that was cut from the final movie. (It's also a punchline which requires an elaborate setup in the preceding lyrics, but that's part of the fun.)
The deluxe version of the soundtrack album includes demos of half a dozen numbers from earlier versions of the show, with commentary by composers Kristen Anderson-Lopez and Robert Lopez, and it's fascinating to see how the book changed during production. There are still traces of the "prophecy" plotline in the trailer above, but it's definitely a stronger story without hokey supernatural predestination.
By the way, Robert Lopez also worked on The Book of Mormon, which is again not surprisingly since he co-created the raunchy puppet musical Avenue Q. And some more connections for you: Christophe Beck, who composed the score music for Frozen (and Buffy the Vampire Slayer, back in the day), was in the Yale Spizzwinks(?) a cappella group alongside not only Robert Lopez, but also Internet musician Jonathan Coulton and my good friend Sean Gugler!
Yes, yes, go ahead: sing that other song that nobody wants to hear anymore.