It's not just the hideous special effects, although those are pretty terrible — especially the closeups of pilots' faces while random rear-projection saucers float around behind them. It's not just the hideous acting, especially the guy who puts way too much processed cheese into lines like, "It's not easy to get away from me." No, it's the fact that you can't tell what the hell is going on half the time during this space battle.
There's just a bunch of close-ups of people's faces, interspersed with random model shots and bits of abstract art. My favorite part is when the camera pans around the faces of the people who are watching the battle from the mothership, as they basically narrate the space battle for us. "Now a dozen saucers have attacked, and you're trapped by the satellites! Roger's gone out of control!"
This absolutely brilliant sequence comes from the incredible 1978 film War of the Robots, which is yet another great piece of Italian space opera from the late 1970s. (Along with The Humanoid and Star Crash, and many others.) This film hits many of the important notes, including having robot/alien people in disco wigs and silver jumpsuits, and having dialogue that's either dubbed or read off cue cards.