After Superman movies showed how to do the perfect superhero film right, they then showed how to do it completely wrong.
The first two films set the gold standard, by being thrilling adventure films with stately craft and a passionate heart. But they weren't entirely flawless. Luthor's aides in
Superman I and the slapstick gags during the Metropolis fight in Superman II veered from humor into vexing camp. Superhero films do best when they are conceived as adult myths of wonder; they are worst when they are tossed off as silly kids stuff. Camp is the path to the dark side.
Director Richard Lester's probable intent was to expand the drama, humor, and romance of the films, but the third film feels dreary, silly, and lackluster. When bad comics films are in doubt, they mug. The feeling of farce drifts into self-parody, losing the dynamic spark and mature wonder that had held the public's faith. Richard Pryor's piercingly incisive stand-up in the 70's had made him as edgy as Malcom X, yet 80's movies like this and The Toy softened him into a goofball. (The bright turn of casting is Annette O'Toole as Lana Lang, and later she brought that light to the Smallville TV series as Martha Kent.)
Conversely, the film attempts to darken Superman, in an evil sequence. You can tell a creator doesn't understand Superman when they try to make him Batman: dark, edgy, conflicted, violent. The actual solution to dramatizing Superman's light is by increasing the darkness of the threat he faces, so that his true strength of character -nobility, intelligence, will, and mercy- proves out and triumphs over it. (Looking right at you, Man Of Steel.) Superman is the avatar of hope in the human heart, and we deserve elegant fables that respect and instill this.