To start off, even though Flesh Gordon has an "X" rating, it is to be considered in no way pornography. Yes, you do see both male and female genitals, and a healthy helping of pseudo-grinding or implied positioning for sex, this film is in no way a Caligula-like experience or hard-core sex-venture. It's not recommended for immature audiences or those with sexual hang-ups or heavy religious convictions.
Believe it or not, the movie actually has a plot and is more than an excuse for simply fapping. Minus the nudity and sexual overtones, this was almost the exact same script used for the first half of the 1980 Sam Jones Version. One laudable aspect of the film is the claymation creature special effects. Equal to Harryhausen's efforts, the scenes with the creatures are wonderful and the rhetoric of Craig T. Nelson (uncredited) as the Monster is on par with that of Alan Rickman (Marvin) in The Hitchhiker's Guide to the Galaxy (2005) and worth the price of admission alone.
Even though the entire movie is a tongue-in-cheek experience, it's still a better production than many of today's modern cinematic endeavors you would find being released via the SyFy channel. If you don't have a large stick up your anus and aren't easily offended by anything outside of the common accepted values, this is something worthy of your attention. It won't be Citizen Kane or Gone with the Wind, but is definitely is better than half of the films you will see released today.