I ike this episode alot, myslef. Sure, it's not the best story wise, but It's excellent comedy-wise, at least to me. The Male/Female jokes weren't funny to me, but most other jokes, such as the Rock Aliens' brutal tests and Zoidberg's "Look it Up" line, made me laugh out loud. Like I said, the storyline could've been layed out much better. I think there was too much attention put on the middle of the episode, and not enough on the end. I'd loved to have seen more of the Crew dealing with their new genders, as I'm sure it would've been hilarious.
In the end, I think it's the jokes that really save this episode, but don't get me wrong, I still lked the story, even if it was put together oddly.
Oh, and I almost forgot...