Adaptation Displacement: The musical is a lot more famous than the original film. It's not uncommon to see people commenting on the Broadway version to say "this story could never work in English!", with resulting "*Cough* *cough* Ahem" responses from people who actually know the movie.
Does Krolock really have some feelings for Sarah and is genuinely guilty of making her one of the undead, but is unable to resist, and turns her for her to become his companion? Or does he just see Sarah as food and is he just clinging to what he thinks is left of his humanity out of boredom, or because he wants to believe he can still feel, and in the end, just gives into his vampire nature and bites Sarah as a metaphorical rape? Is he still clinging to his humanity, or is "Die unstillbare Gier" a charade?
Does Sarah really know what she is doing all along? Is she in love with Krolock? Is she just some Bitch in Sheep's Clothing trying to get what she wants by manipulating Alfred and Krolock? Or does she coax herself in the belief that Krolock is just some twisted prince charming with whom she's infatuated and who can grant her freedom, to discover, in the end, that he just manipulated her all along?
Is Herbert really infatuated with Alfred? Or does he just see him as food and just isn't as subtle as his father is?
On that theme: Is Alfred really interested in Herbert without knowing or consciously acknowledging it? note (See Krolock's comments in Vor dem Schloß about morality and hidden lusts/longings. Interestingly enough, said lines are delivered to Alfred after Herbert has appeared onstage, so there is a fair chance the attraction is real and Krolock isn't just playing mind games to get Alfred to give in. Or he's just tired of his son's boredom and ships Alfred/Herbert as a consequence.) Or was his (possible) hard-on in Wenn Liebe in dir ist just a physical reaction that he can't control, since for all intents and purposes from Alfred's point of view, Herbert was assaulting him?
There's no denial of course that Chagal is an Abusive Parent, but considering that outside is not freedom, but hungry vampires who have a thing for young maidens, is his behavior towards Sarah at the very least understandable?
Awesome Music: "Carpe Noctem", which features three groups singing two languages for ten minutes, and "Der Tanz der Vampire".
Berserk Button: Think the Broadway version isn't as horrible as so many make it out to be? Great! Just, uh, don't tell anyone. There's a chance they might share the opinion, but it's far more likely you'll get Punched Across the Room (or at least the internet equivalent).
Big-Lipped Alligator Moment: So, the whole musical's in German/Hungarian/Dutch/Estonian/Japanese. You're listening to the finale, when all of a sudden, the vampires start singing in English. Before you can realize that no, you're not just hearing things, they've gone back to German/original language. It never happens again, and is given no explanation. Apparently, the lyrics were kept in because Steinman's original English demos were too good to not keep at least some of them in. The Polish production didn't feature the English lines there, and while Japan left them out of that part, it did have some Gratuitous English in other places.
An English-language version of Carpe Noctem, titled Seize the Night, was recorded by Meat Loaf in 2006.
Reverse example: Most people in German-speaking countries know the Tanz finale as, well, the Tanz finale, without realizing its basis in Streets of Fire and "Tonight Is What It Means To Be Young".
Same with "Totale Finsternis", as opposed to the original "Total Eclipse of the Heart". It helps that the friggin' vampire love duet makes more sense than, and is far less narmtacular than, the original Bonnie Tyler song.
"Die unstillbare Gier" had a first life as "Objects in the Rear View Mirror May Appear Closer Than They Are" on Meat Loaf's Bat Out of Hell II. Unlike the others, this isn't a complete lift - the two songs have different choruses and "Die unstillbare Gier" is a verse shorter.
As the other wiki points out, about 70% of the musical score written by Jim Steinman was recycled from his earlier projects, mainly from his less-known shows written in the late Sixties and early Seventies before he abandoned theater to work with Meat Loaf. As the Loaf himself says in his autobiography of Jim's songwriting process for albums, "The way Jim works on an album is this: First he recycles stuff that's either been lying around or, often, songs he's used elsewhere in another form. [...] Steinman regurgitates the older material, then he writes three or four new songs, and that makes the album new. When he has the content down, then the album is ready to be recorded." That's pretty much what happened here. Steinman even speaks at the link provided of having written the score in a month, which would be near impossible for an established theater composer without recycling (or at least going through a few more drafts later in the process).
Draco in Leather Pants: Both of the von Krolocks are prone to this. On a greater scale, Tanz!vampires in general. It's established in the final scene that Alfred and Sarah are as bad as any of the other vampires throughout the show once they've been turned, but try finding any fic set afterward that doesn't show Alfred as a meek, befuddled vampire, rather than a snarling beast whom Sarah restrains from immediately attacking the Professor just so she can convince him to help her spread their plague through the world instead.
"Dies irae Kyrie, libera me domine. Dies irae Kyrie, requiem da domine..." It is made worse by the fact that those two lines have the same melody and are repeated again and again.
"Sei berit! Manchmal in der Nacht fühl' ich mich einsam und traurig, Doch ich weiß nicht, was mir fehlt..." Just try listening to the original "Total Eclipse of the Heart" without hearing "Totale Finsternis" in the back of your head.
Ensemble Dark Horse: A textbook example. Herbert has one line in the first act, shows up for one scene and song in the second, and only appears in the ensemble for the rest of the show. He is not all that important to the plot, but even the press release for the Vienna revival calls him the show's most popular character. This also qualifies him as a One-Scene Wonder, as seen below.
Even Better Sequel: A lot of the fandom considers the Hungarian and Russian productions to be better than the original, mainly because of the more dramatic props, costumes, and staging changes.
Fan-Preferred Couple: There aren't that many Alfred/Sarah shippers out there. Most fans seem to prefer Sarah with Krolock, and a strong number like to pair Alfred with Herbert. Anyone who's seen the film beforehand ships Krolock/Professor with renewed vigour, some fans going so far as to state that 'Gott ist tot' is aimed at the Professor, not Sarah.
Heartwarming Moments: "Für Sarah". Even if, as an audience member, you're screaming things at him like "This is ridiculous - she doesn't deserve you!", "You idiot, you're gonna get yourself killed!" and, if you've seen the show before, "Come on, even Herbert would be a better match for you!"
Both of the leading men of The Phantom of the Opera went on to originate the role of Graf/Count von Krolock, Michael Crawford (the Phantom) on Broadway and Steve Barton (Raoul, vicomte de Chagny) in Vienna. The leading ladies of Phantom and Tanz are brunette ingénues associated with the name Sarah (Christine Daaé, played by Sarah Brightman, and the character Sarah Chagal.) Crawford's production tanked, whereas Barton's production was successful, award-winning, and has spawned multiple international versions and German revivals. Guess the universe supports Team Raoul, after all.
The overlap of cast members between Elisabeth, Tanz, Rudolf: Affaire Mayerling, and Ludwig II's musical makes Ludwig's presence at the ball hilarious. For example, Lukas Perman and Marjan Shaki (Alfred and Sarah) were Rudolf and Helene von Wittelsbach. Jan Ammann (Krolock) was Ludwig. Drew Sarich (Krolock) was Rudolf in Affaire Mayerling. Mark Seibert (Krolock) was Death.
The kicker? Ludwig is Elisabeth (Sisi)'s cousin, and the two were very close. In a case of What Could Have Been, Sisi was considered as a possible ball guest in the new costume designs (wearing the famous Star Dress), but this idea was scrapped.
Koukol looks quite a lot like The Hunchback of Notre Dame. Drew Sarich (Krolock) wound up originating Quasi in the first German-language production of the stage show.
In "Knoblauch" Chagal sings that garlic turns old men into Romeos. A few lines later, Alfred enters - in the first Vienna revival, played by Lukas Perman, fresh off his role as Romeo in Roméo et Juliette, de la Haine à l'Amour. With Marjan Shaki (Sarah) as his Julia.
Even funnier: That means Tanz is the second time Perman and Shaki played characters who die at the end.
Hollywood Homely: The Polish!Rebecca◊ and Finnish!Rebecca simply looked like older and much heavier versions of Sarah, wavy brown hair and all, making it extremely easy to imagine her having been a beautiful young woman years ago who just aged through a difficult life.
Ho Yay: It's implied that Alfred is physically attracted to men when the Professor looks at Alfred's crotch after the incident with Herbert and announces "I see how things stand!"
The Japanese production's finale implies that Alfred and Herbert end up together after Alfred is turned into a vampire too.
Something similar was suggested in the final performance of the show in Hamburg, where the actor playing Alfred wandered out onstage during the finale and the actor playing Herbert promptly broke out of the choreography to kiss his throat◊. He even joins in the choreography towards the end. (around the 3:20 mark)
From the new Vienna cast recordings: Lukas Perman manages to make Alfred's screaming as Herbert and later Sarah attacks him seem borderline sexual. It's less obvious in the former scene because Professor Abronsius comes to Alfred's aid fairly quickly, but in the latter, there's nothing but the background music and the sounds he's making.
Some German actors also play this kind of tension between Count von Krolock and Alfred in "Vor dem Schloß".
In the dancing scene in "Carpe Noctem", things happen between the white vampire (Alfred's symbolic stand-in) and the black vampire (Count von Krolock's symbolic stand in).
Well, the Count did say Alfred's soul belongs to him...
There's often a male vampire in the ensemble that Herbert seems to be interested in during "Tanzsaal". In the Russian version this is Ludwig II of Bavaria.
Never Live It Down: Herbert calls Alfred "mon chéri" exactly once. In many fanfictions Herbert seems to be unable to call Alfred anything else.
Vampire Chagal and Magda becoming a couple, when she was clearly uncomfortable with his advances while they were alive. "Geil zu sein ist komisch" may induce cringing with its talk of humans only being an animal with a natural instinct for sex.
Even if the Double Standard: Rape, Male on Male is omitted via some of Herbert's actors playing him as genuinely infatuated with Alfred but simply poorly socialized, the Professor still victim-blames by asking whether Alfred provoked Herbert, checking whether Alfred has a hard-on with a magnifying glass aimed at Alfred's crotch, and being dismissive when an indignant Alfred insists that it was all Herbert.
Severely dependent on the actor, but the musical depicts Herbert much more sympathetically than the movie, and certain actors have milked this for all it's worth, causing the audience to feel very sorry for him upon being rejected.
Some actresses portraying Sarah can pull this off during the ball scene.
Covered Up: Again, and one that wasn't in the original. Large sections of "God Has Left The Building" (the opening vampires' dance) are taken from "The Opening Of The Box" from Steinman's project Pandora's Box. (Which was also the group that gave us "Gott Ist Tot", "Einladung zum Ball" and "Tanzsaal".)
One-Scene Wonder: In a reversal of Herbert's screentime, they appear for one scene and song in the first act, then have one line in the second act.
Replacement Scrappy: Since he got rid of a character instead of being a different version of an old one, Boris got a lot of hate from fans.