If you're of the opinion that the concept of a Horror Musical is just too goofy to work, you're absolutely right. The genres are too at odds to play together and create anything but an unwatchable mess. But throw in a 3rd genre, and you're on to something.
Stage Fright is a Horror-Comedy-Musical that works precisely because the horror is dialed down to the point where it's not actually a horror film, but a horror-themed musical comedy. While there's nothing scary about Stage Fright, there is some pretty decent gore that will keep the sickos among us happy.
What's most surprising about Stage Fright is how well is holds up as a musical. The songs are insidious ear-worms that get lodged in your brain for weeks at a time. I've spent the last five days spontaneously bursting into the refrain, "I'm gay, I'm gay, but not in that way." And the film's lead, Allie MacDonald sings the living shit out of her songs. Stage Fright even boasts an opening starring the all-singing, all-acting Minnie Driver, who suffers a wonderfully horrible murder in her dressing room.
Stage Fright takes place at a youth theater camp called Center Stage that is run by Meat Loaf Aday, which is, of course, the mark of quality. Theater geeks should be just as into this movie as horror geeks, because it directly caters to them. Center Stage is populated by theater-geek caricatures who have found their refuge, a place where they are free to express their innermost selves without fear of abuse from peers and parents. Then, of course, the fear begins.
One of the movie's cleverest gags is that whenever the killer sings, he does so in an over-the-top metal wail, backed by searing doom-metal guitars.* When he delivers his pre-kill one-liners, he does so in that same ridiculous voice. The one-liners are all theater-related cliches so awful that they become highest art. And please do yourself a favor and listen to the closing credits medley with every song performed by this same metal band. It's a trancendant experience.
For a movie about the brutal murder of teenagers, Stage Fright is a fun, light-hearted romp that will keep you laughing until ear-worms make your brain explode.
*Full disclosure: I don't know Deathklock from Mastodon, so I'm pretty sure I've mislabeled the metal sub-genre.