And You Thought It Would Fail: With massive Executive Meddling from Paramount and the MPAA and interest in the show waning after only the second season, Trey Parker was convinced that the film would be a major flop and made it as a last hurrah for the series. Instead it was a commercial success and critically acclaimed as a smart and funny satire and greatly raised attention to the show, which has now taken The Simpsons' place as the gold standard of modern American satire.
Awesome Music: The whole soundtrack, particularly "Uncle Fucka", "Blame Canada", "Kyle's Mom's a Bitch" and "What Would Brian Boitano Do?" (especially the DVDA version)...
Cry for the Devil: A literal, Miltonian example - Satan is one of the most sympathetic characters in the entire film.
Dancing Bear: Surprisingly for a movie based on a poorly-animated adult cartoon, the movie perfectly apes the style of big Broadway productions and Disney Renaissance films, and still allows it to stand out among the more recent and topical TV seasons.
Ear Worm: All the songs, but especially "Kyle's Mom is a Bitch" and "Uncle Fucka".
Ensemble Darkhorse: This movie is Ze Mole's only appearance in the entire series. He appears for roughly 15 minutes. He is by far one of the most popular subjects in "South Park" fan-fiction and fan-art.
Fridge Brilliance: Kenny saw and eventually entered the Muslim version of heaven, since there were 72 virgins waiting for him.
It wasn't really anticipated, but Kenny's Heroic Sacrifice becomes a lot less poignant after watching the "Coon and Friends" trilogy, where it's explained that he comes back to life every time he dies, so it wasn't a very big sacrifice for him to go back to Hell.
During the Oscars, Robin Williams sang "Blame Canada" as Mary Kay Bergman, the voice actress of nearly all the characters who sing that song, had committed suicide earlier due to serious depression. In 2014, Williams would also take his life for the exact same reason.
Seeing Saddam Hussein in Hell with Satan becomes funnier after his eventual execution.
A censored family friendly version Terrance and Phillip: Asses of Fire is replaced with the original and is only one minute long. A couple years later a family friendly PG version of Freddy Got Fingered that was three minutes long was featured as an extra on VHS and DVD.
When Terrence and Phillip are strapped into their electric chairs, Terrence comments that his is worse than Phillip sucked on his dick and took a picture. A similar situation would happen in the episode "Cartman Sucks".
"Blame Canada" is Sheila's Villain Song and establishes her and the other moms as enemies of Canada (including Terrance and Philip). Years later, South Park: The Stick of Truth plays the song when the player character goes to Canada with the other kids to get help from Terrance and Philip, among other Canadians.
Likewise, the popularity of Nickelback and Justin Bieber make the song even more hilarious, and it's Cartman, one of the heroes of this movie, who gets Biebs killed in a later episode.
Another one from The Stick of Truth. Kenny hardly sings in this movie (he only gets a few lines in the first "Mountain Town"), but his "Furry Friends" attack in the game has him briefly sing a song while summoning his rats.note The only other party member who sings is Jimmy, who didn't even exist when this movie was made. The real kicker is that Furry Friends is an example of Disney Creatures of the Farce (complete with Kenny as a princess), which is based on the very thing thatBL&U is parodying.
When Cartman angrily demands "Who wants to fucking touch me?!" after seeing the Terrance and Philip movie, Butters (at that point an unnamed background kid) is the only one to do so. Rewatching this scene years later, after seeing their dynamic in later seasons makes it doubly funny.
Even Satan, despite being considered as evil by default, is sympathetic.
The Mole. He clearly didn't have the happiest childhood, considering the fact that his mom apparently tried to abort him on her own with a clothes hanger and it's implied that she's abused him ever since.
"HOW WOULD YOU LIKE TO SUCK MY BALLS, MR. GARRISON?"
"It's fucking Windows '98!"
Misaimed Fandom: Mr. Garrison claiming that he "doesn't trust something that bleeds for five days and doesn't die" was a jab at sexist views on periods. People are now quoting it unironically.
Moral Event Horizon: Sheila crosses it when she shoots Terrence and Phillip dead, even after Kyle tries to reason with her. Her buildup is also MEH-worthy, starting when she orders guard dogs to maul a boy not that much older than her son. Then, when the rest of Mothers Against Canada see the bloodshed as a result of the American-Canadian war, Sheila is still convinced that she did the right thing.
Could've been worse... In the 8th draft of the Script... she wanted Ike, Cartman and Kyle executed along with Terrance and Phillip for being "Canadian Sympathizers" and Cartman's mom was ok with it while Stan and Kenny's mothers were shocked by this act.
Her crossing also leads directly to Sadam's own crossing of the MEH when he declares himself ruler of the world and tries to have everyone killed, completely betraying Satan in doing so.
Retroactive Recognition: Non-actor example: Butters appears several times through the film, but wasn't even named at the time.
Rule of Funny: The only real reason the Mole is in the film at all.
Seinfeld Is Unfunny: While the movie is still well-loved and stands out from the rest of South Park for being an all-out theatrical-ish musical, some fans find the more recent TV seasons to be more entertaining and/or relevant because they deal with more recent and familiar topical humor (and also have animation that's had years to mature since BL&U).
Strawman Has a Point: Sheila and the other moms early on, as their kids were indeed being badly influenced by the movie and that Kenny died imitating a stunt from it. They only become villains (well, Sheila, anyway) when they decide to blame Canada for their troubles.
We must blame them and cause a fuss Before somebody thinks of blaming us!
What an Idiot: Pretty much Sheila had, by far, created one of the most idiotic and disastrous acts. She went to extremes to make the world a better place for hers and everyone else's kids by having Terrance and Phillip executed and start a war against Canada, when she could've just created a petition to get the Terrance and Phillip movie banned from their country; or, alternatively, a petition to actually enforce the age restrictions that the movie already had.
Did we mentioned her adopted son Ike was CANADIAN? Even Kyle pointed this out, who knows how she would've reacted if Ike was put in a Concentrat... I mean a "Happy Camp".
The Woobie: Kyle, who has to save the world from a misguided moral crusade started by his own mother.
Terrance and Phillip, who are arrested, sentenced to death, and ultimately shot dead, just for exercising their 1st Amendment rights (or whatever Canada's equivalent is). Technically, they did end up killing a child, but considering the kids were watching the movie without permission, and were emulating a scene where a character dies doing the exact same thing thus suggesting it was a bad idea...