Phantom of the Paradise (1974)
Part musical, part body horror, part morality play, part meta commentary about the corporate machine, and all while paying homage to classic horror films and stories of the past including Phantom of the Opera, Dr. Caligari, Faust, Dorian Gray, and more.
Phantom of the Paradise was written and directed by Brian De Palma, who would go on to bring us the horror classic Carrie. To get to the point, his work on Paradise is amazing. The film moves at a breakneck pace, it uses the split screen to even better effect than Carrie, and is filled with colorful performances that in hindsight would echo the style we'd see in Scarface a decade later.
Also, we have to mention actor and songwriter extraordinaire Paul Williams who penned every song in Paradise and who steals the show as the suave villian Swan, but would you expect anything less from the man behind "Rainbow Connection"?