Science Fiction; Adventure; Allegory
Star Trek pretty much wrote the book on hard science fiction. Unlike Star Wars, which takes its futuristic technology with a side dose of mysticism, Star Trek tries to paint a more realistic picture.
There's a bit of New Age hokiness, true, but the movie is primarily rooted in scientific truth, rather than something nebulous like "the Force."
In addition, Star Trek features many aspects of an allegory. This makes sense, as one of the primary purposes of science fiction is to comment on the present by talking about the future. It's an allegorical genre by nature.
To this end, the original series commented on everything from racism to nuclear war through the lens of the distant future. The Motion Picture, on the other hand, tackles themes of technological growth and the nature of consciousness.
It's also worth noting that the film (and series) takes heavy cues from classic adventure stories, especially those of the swashbuckling variety. Think about it—the Enterprise is basically a naval vessel. The crew just has laser guns instead of swords. When viewed through this lens, the film is revealed to employ many character archetypes and thematic elements from the classic adventure tales of yore.