Continuity mistake: Behind where Nuclear Man lands there's no school bus on the wide shot, which is a matte painting, but a frame later one appears and stays there for the rest of the scene.
Continuity mistake: Clark enters the barn to fiddle with his green crystal. When he exits, a huge amount of stuff from his childhood has magically appeared around the place.
Revealing mistake: Watch the moon fight between the two supermen. In one scene, Superman charges nuclearman and you can see the backdrops flutter if your monitor brightness is high.
Plot hole: For some strange reason, when Nuclear Man passes away in space, he remains floating, however Lacy, who is grabbing his hand, falls downwards.
Continuity mistake: The close shot of the Great Wall exploding shows an edgy architecture, with straight lines. The wide shots show a curvy construction.
Continuity mistake: After Superman lets go off the elevator on the surface of the moon, the cables fall down with the elevator, but in the close-up the cables are up and fall down again.
Continuity mistake: A couple walks behind the hot dog stand in the same direction twice in less than half a second.
Continuity mistake: In the barn, Superman puts a glowing crystal inside a pocket. A frame later it disappears.
Continuity mistake: Luthor holds a sealed champagne bottle with both hands on the neck of it. He doesn't move them, nor his shoulders, nor do we hear any sound revealing that the bottle's being opened. However, when Luthor leaves, the bottle's seal appears opened and 20 centimeters away when the scene ends.
Continuity mistake: When the truck is carrying the missile, the officers parading in front of it pass by the same place twice.
Continuity mistake: Before Superman enters the UN hall, the amount of people by the staircase changes between shots.
Continuity mistake: During the volcano eruption scene, an old man with a black hat on the right appears and disappears depending if the shot is a close-up or a wide shot. This even happens when the shot changes follow one another immediately.
Continuity mistake: While Superman is taking the Statue of liberty back to its place the sky keeps changing between violet and blue, sunny and cloudy.
Continuity mistake: When Superman leaves Luthor in the quarry, he lands several feet to the right of the cop. In the close-up they are almost close to each other.
Continuity mistake: Shortage of extras in this film: Inside the UN hall, the arab man that greets Superman is the one that a second before was in the entrance, together with the woman with a pink handkerchief over her head.
Continuity mistake: When Superman lands Lex on the quarry, the standing position of the prisoner behind differs between shots.
Continuity mistake: After the two police cars are sent backwards, a third one that was parked behind, suddenly appears aligned with the other two.
Continuity mistake: When Lois is in the subway carriage crying for help, she places her right hand on the rail above. A frame later the hand is by her waist.
Continuity mistake: Before lava covers the Italian village, furniture under the two arches on the right, as well as a vase, cart wheel and table on the left disappear between shots.
Revealing mistake: When NuclearMan goes to destroy the Great Wall of China, there is a brief glimpse of him wearing support wires.
Answer: It was made on a very low budget. Golen - Golbus productions bought the rights to Superman. They were mostly known for B-Movies with not so big name stars. It was there attempt to play with the big studios. Plus at least 45 minutes of scenes were cut out, with major subplots.
In addition to budget cuts, they kept shortening the runtime, meaning scenes needed to be cut. The comic book adaptation has the uncut scenes and makes much more sense.