In order to keep the phenomenon going Gene Roddenberry knew he had to have something special to offer and he did. The continuity from the television series was accomplished effortlessly, in fact one of the new characters Commander William Decker is the son of William Windom who was another starship captain in an episode. More I can't say less I give the plot away.
In fact Decker played by Stephen Collins would be commanding the newly fitted Enterprise if it were on a routine mission. But with the threat of an immense alien being on a direct path to earth now Admiral James T. Kirk takes command of the starship himself and with Decker reunites all the old crew from the TV series to meet the threat.
Fans of the original series will also see the similarities in plot between another episode involving the Enterprise meeting up with an old space probe that now has taken on some new functions. The same idea forms the basis of this film's story although in every way it has been expanded and a new ending conceived. Here's a hint, a budding relationship between Collins and new ship's lieutenant Persis Khambatta is what ultimately saves the earth.
Just as you remember them William Shatner, DeForest Kelley, Leonard Nimoy, James Doohan, Nichelle Nichols, George Takei, and Walter Koenig are all back and completely in character as you remember them. The new people Collins, Khambatta and the rest are integrated nicely into the story.
Star Trek: The Motion Picture received three Academy Award nominations, for Best Art&Set Direction, Best Visual Effects, and Best Musical Score. The special effects never overwhelm the telling of a good story which is the primary mission and best asset of the original television series and its successors.
If you're not a Trekkie before seeing this film, you may be come one upon viewing.