If you ever decide you want to see it please for the love of Tim Curry don't watch it on TV.
The only way to experience the RHPS is at a theater, movie or stage, with a floor show. Without the floor show you will not get what makes RHPS an adored Cult Classic. Seriously, the floor show is what makes (or breaks) the experience.
If you walk into the show and you're not surrounded by people in costumes spouting weird lines, or if you don't see them in the aisles within the first 90 seconds of the show starting then you may as well get up and leave.
The same thing applies to The Room, another terrible movie turned cult classic. You need to be in a theater of people throwing spoons or it's not worth watching.
It's quite a thing, that could only be a product of the 70s. Might make you go "huh?", and is almost certainly the only context I feel comfortable with the word transvestite today.
If you decide to watch the movie, I advise against watching it at home. In my opinion what makes the movie special is what fans have built around it, and you need a movie theater to experience that.