Continuity mistake: When Lois opens the terrace doors in the hotel suite, the angle changes and the furniture on her right moves several meters to the left, appearing close to Lois.
Continuity mistake: In the gym, a man leaves a towel on a low wall. Watch the blue and grey stripes and you'll notice that its position is different between shots.
Continuity mistake: When Superman flies away from the tower holding the elevator, the first angle shows him leaving towards a 10 o'clock direction. A frame later the position of the cable shows him leaving to a 7 o'clock direction.
Continuity mistake: When Nuclear Man and Superman fall off the balcony and fight, the position of their bodies has no continuity in the wide and close shots.
Continuity mistake: In the quarry, the cop on the right's hat has two strings around the top, the upper one dissapears depending on the shot.
Continuity mistake: The UN building that Superman walks towards and the one he arrives at in a new shot look entirely different.
Continuity mistake: When Luthor introduces Nuclear Man to Superman, a towel on a chair changes from ironed and flat to a big bundle in less than a second.
Continuity mistake: When Nuclear Man is about to land on the Great Wall, the aerial view shows it's empty; a second later it's filled with people.
Continuity mistake: Nuclear Man sends the 2 police cars back and the one on the right skids and faces slightly to the right, but a second later, when they explode, both cars are perfectly aligned.
Continuity mistake: When Lacy shows the mock front page of the Daily Planet she holds it covering the red circle on the top right. A frame later she's holding it several inches down.
Continuity mistake: When Nuclear Man sends the police cars back, there's a man close to a mailbox on the left. There's a very brief cut before the cars explode but when the explosion takes place, the man has vanished.
Continuity mistake: Nuclear Man lands on a street surrounded by skyscrapers. In the following shots where he destroys everything, the right side of the street is the same, but the left side is totally different: small houses, sunnier, signs on the walls.
Continuity mistake: While the volcano explodes close to the Italian village, a man jumps off a balcony but disappears just a frame later from the following wide shot of the place.
Continuity mistake: A couple seconds after Lenny insults Nuclear Man, when he is about to be lifted up, the place he stands in is different from where he was before.
Continuity mistake: In the hotel, right before Lacy enters the elevator, the hall of the hotel is filled with plants, couches and people. A second later, while Clark is on the trolley, the hall is a vast, empty place for the trolley to wander around.
Continuity mistake: When nuclear Man watches the newspaper on the table, the lighter is by the side of the phone. In the following shot it's in front of it.
Continuity mistake: When Lois gets in the train, the people next to her change completely between shots.
Continuity mistake: Before Superman rebuilds the Great Wall, he flies up with a woman in his arms. He flies past a stone arch and starts to descend. However, the following angle shows him yards behind descending right by the center of the arch.
Continuity mistake: Before Lex presses the red button to launch the missile, the phone next to it is hung-up. Then someone grabs it and the phone cable covers the control panel, but the immediate close-up of Lex's finger shows that the phone is hung-up, as in the first position.
Continuity mistake: The bundle that Superman makes to destroy the weapons changes to a tenth of its size in about a second.
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.