A Mega-Sized Star Trek Episode
Structurally speaking, Star Trek: The Motion Picture isn't too different from the television series that preceded it. That's kind of unusual when you think about it. Most movies based on TV shows break hard from their preexisting formulas—even most Star Trek films.
As we learned in the Screenwriters section, however, this is mostly based on circumstance: Star Trek: The Motion Picture was based on the pilot episode of a planned Star Trek series. There were some major changes made, of course, but we're still dealing with the same base elements.
That being said, we haven't really talked about how this thing is structured. Well, it's nothing fancy. We follow one main story arc with a few tiny side branches along the way, with the plot pushed forward by big events (entering V'Ger, discovering Robo-Ilia, etc.) rather than by individual character arcs.
Similarly, the film doesn't have a tightly-shut ending. Instead, it leaves things open, promising future adventures for Kirk and the newly reunited crew of the Enterprise. This again harkens back to the original series, which always left our heroes ready for a new adventure by the end of the episode.