There are many ways in which a bad movie can be fun to watch. These include having a bad guy that you can still hate, dialog that fails spectacularly, or ridiculous glitches. There are WTF moments and inexplicable plot holes. Sometimes there are characters that totally surprise you, or well-done scenes hidden in the general badness.
There can also be the ironic appreciation of cheesiness, usually if that cheesiness is sincere. Finally, some bad movies can be appreciated specifically for the gratuitousness of the violence or sex that was stuck in to spice it up.
Barbarella doesn’t have much to offer. There is some nudity, and Jane Fonda is certainly attractive. But in general the scenes are more slow than they are ridiculous. None of the villains are interesting or hate-able. Though I should mention that the band Duran-Duran is named for one of the bad guys.
It is cheesy, and that can be interesting. The sets and costumes are worth checking out, though the horrible music makes the experience difficult. I would recommend watching this if you are a film student or interested in the history of the sixties and seventies. Otherwise there are some real bad movies out there that would better reward your time. I give it two stars out of five.