I remember this movie very well. I thought it was a great follow-up to Superman I & 2, though some parts could've been improved. I would've loved to see an extended fight scene between Clark Kent and the evil Superman in the junkyard along with more character development scenes with Clark Kent and Lana Lang. Also, the cyber-woman scene near the end has always scared the crap outta me since I was six-years-old, though the special effects were very nicely done! Obviously, not the best Superman film, but far better than the horrible Superman IV.
I love this film. My favourite scenes include the battle scene between evil Superman and good Superman and when he enters that cave with the big computer to confront Ross Webster and others. A good classic comic book adventure sequel.