I loved the whole Superman side of the story in Donner's film. The origin story, the time in Kansas, the training in Fortress and the Clark Kent in Metropolis story was great. I also liked the variety of action in the finale.
That said, the one thing that REALLY dates the movie for me was the characterization of Lex Luthor. I guess that was a valid portrayal of the character from some of the comics, but it wasn't my preferred version. Here is supposedly one of the smartest people on Earth and he surrounds himself with the two dumbest people he could possibly find. He seemed more like a used car salesman than a villain in a superhero film. He never seemed much of a match for Superman. That's one of the reasons I was excited that Kevin Spacey was cast in Superman Returns. I expected something closer to the character in the animated series or Michael Rosenbaum in Smallville, but instead we got a rehash of Hackman's role.