When I first saw Superman, I was quite young (8), and went to the theatre in a Superman costume which, if I say so myself, was designed with flawless detail (better than the one used in the movie). Needless to say, I was the center of attention at the theatre and while I wasn't bothered by it then, I get embarrassed today thinking about it.
I used to collect Superman comic books regularly, up till his death at the hands of Doomsday and the subsequent revival a few years ago. That is how much I cared about the myth. While the comic book itself has changed over time, it is the old Action Comics, simplistic by today's standards, that I go back to re-read over and over again. The same charm that is resent in old Action Comics is captured quite accurately in this movie.
Superman makes a nice introduction to the super-hero (Christopher Reeve), not only setting the stage for Superman 2 by introducing the Phantom Zone, but essentially sticking to the comic book history with characters like Jor-El (the father of Kal-El (aka Superman), played by Marlon Brando), Jimmy Olsen, Perry White, Lois Lane, Lana Lang, and of course, Lex Luthor (Gene Hackman).
The movie spends the first hour introducing the myth, which I think was an excellent move. The rest of the movie is just filler, with a plot involving Luther who intends to make a killing (literally) on the real estate market. The acting is okay, with some decent performances by Reeve and Hackman. The dialogue itself appears quite cheesy in this day and age, particularly Superman's commitment to "the American way" and lines like "the country is safe again, Superman, thanks to you!" (It somehow sounds incongruous said verbally on the screen instead of read in a comic book.) However, I'd say it is a necessary prerequisite-requisite to watching the upcoming re-make of this movie.