For an adult, well, the plot, physics and acting have a few problems that negate the childhood nostalgia. The plot had no real problems with it other than connecting the dots better. Had it been tighter I think many of the other problems would have been less of an issue. Physics is another big problem, there are a number of scenes towards the end where either the black hole's gravity of vacuum of space should have presented bigger problems when the Cygnus was falling apart. Lastly the acting was a little flat, but that might be due to the problematic script if rewrites were all to common.
The special effects, even by today’s CGI standards, is good. For 1979 they were great! It might have been nice to see Disney revamp some of the effects with CGI, like BBC did with Red Dwarf. The sets are well dressed and the effects around them are good fun (so long as you ignore some rules of physics). From an RPG perspective it gives a good campy set up for an installment in a campaign or multi-session stand alone effort. If anyone in your group is under the age of thirty there is a good chance they have never seen The Black Hole, which will likely help. But even if they have seen the film there are so many plot tweaks that could be added (and likely should have been added to the film) that it could prove to be an enjoyable experience.
The Black Hole is still good fun, twenty years later, but it is hardly a classic science fiction film in the manner Star Wars or Star Trek II might be.
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