Well, it is an Italian production - though there was a German cut that I think was shorter.
Also also, a synth-heavy soundtrack that has some Wendy Carlos-ish moments.
Also, there's nudity, and scenes of fornication with obvious body doubles. Especially in a forest where meanwhile one of the blondes is chased through a forest full of birches by a faun-creature with it's phallus all out in the open. Eventually they get around to having a zap-gun battle with these guys.
Isn't this one of the many films that stole footage from Star Wars in some parts of the movie? I can't think of another reason why one of them would be wearing Han Solo's getup.