Yup, the movie sucks. That's why making fun of it is so fun.
I've seen the ghastly show forty-odd times, almost all at the Loews^H^H^H^H^H Sony theater in Harvard Square, where it's been playing regularly for years and years. My dad brought me the first time - he had never been before either. I was a regular the summer I was 15-16 (snuck in as often as I could, got my dad to buy my ticket sometimes). After seeing the ceremony by which first-timers were anointed with a red "V" on their foreheads and publicly humiliated before the show (the stage Frank-n-furter puts a red balloon, a symbolic cherry, between the Rocky-Horror-Virgin's legs and pops it with his teeth), I systematically brought all of my friends to the show and, one by one, got them up on stage and sacrificed. The best part was that they'd dress the poor schmuck up in a bridal outfit and have them play the bride during the first scene.
I had a math class with the girl that played Columbia on the stage in front of the screen. She was behind in math; I was ahead. I did her homework a few times in return for free admission and a chance to say hi to the "stars" of the stage show. I remember the thrill I got when one of her nipples briefly escaped her gold sequined top.
The Harvard Square cast is dedicated, and mostly good actors. They'll let random people play Rocky, though, so he's always a toss-up. The crowd there is also dedicated - most of them know funny things to scream, and they rarely get the timing screwed up. All in all, I highly recommend it.
They've been facing increasing opposition from the theater, though. They decreased the showing from 2 a weekend to 1 a weekend, and were even threatening to go to 1 a month, which would be a real tragedy. Help support them, have some fun, and laugh at a friend in the process.