It's a musical turned movie musical; the film didn't do well on initial release. HOWEVER, it did well on the midnight movie circuit and from there it garnered a sort of word of mouth cult following that allowed it to become a big hit and pop cultural phenomenom. Especially with the "interactive" version; where a bunch of people who saw the film regularly at theaters came up with an "interactive game" where you yell stuff at the theater and bring/throw stuff at the screen.
The film's message ironically is pretty much anti-degeneracy; Frank N Furter is not a hero but a villain who does all sorts of bad stuff (rape by deception on Brad and Janet, mistreating his flunkies, abusive towards Rocky when his sex toy starts to disobey him, murdering Meatloaf TWICE and serving his flesh to Brad, Janet, and others). The final song even spells it out with Riff Raff telling him "his lifestyle's too extreme" for normal garden variety types like Riff Raff and Magenta, both of which come from a planet where crossdressing and androgyny is considered normal and socially accepted. It also shows the good and bad side of letting go of your sexual inhabitions: Brad has a nervous breakdown while Janet embraces being slutty.
In that regards it's pretty red pill in the idea that while some fetish/crossdressing is OK and healthy, that when you go overboard and start forcing it onto others, then you go to far.