The Biggest Problem...
I think the biggest problem this film faced was planning.
There are often films that come out around the same time, and have reasonably comparable budgets, and the one that looks cheaper, invariably seems to have been made on the fly, without planning what could be done.
It appears Superman IV just pushed ahead with the plot as if they still had $36 million to use, forcing effects and sets to look insanely cheap.
Had the production taken a figurative minute to replan the film when faced with a budget reduction (excise one of the Nuclear Men from the beginning for example), it wouldn't necessarily have been a "great" film, but way better than what we got.
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