Star Trek IV: The Voyage Home

Star Trek IV: The Voyage Home is a 1986 science fiction film, and the fourth film in the Star Trek movie franchise.

Plot
The former crew of the USS Enterprise decides to return to Earth and turn themselves in for their actions in stealing and destroying the ship in order to resurrect Spock. Before they can arrive, however, a mysterious alien probe shows up at Earth, immobilizes all nearby starships and space stations, and begins vaporizing the planet's oceans. Spock determines that the probe is not intentionally trying to destroy the planet, but attempting to communicate with humpback whales, which went extinct two centuries previously. This leads to the crew taking the Klingon Bird-of-Prey which they stole during their rescue of Spock back to 1980s America, where they land in San Francisco and begin looking for a pair of suitable whales.

Why It Rocks

 * 1) The film carries an environmental message, and aside from one or two brief moments manages to do it without feeling overly preachy.
 * 2) Dr. Gillian Tyler (Catherine Hicks) is a funny and endearing character and the only real romantic interest that William Shatner's version of Kirk gets in any of his film appearances.
 * 3) A lot of funny jokes poking fun at 1980s America and the Cold War.
 * 4) The way the main characters travel back into the past is a neat call-back to the original series episodes "Tomorrow is Yesterday" and "Assignment: Earth".
 * 5) Spock has a nice story arc, finding his human half again after being restored to life in the previous film. It eventually results in him being the first one to suggest rescuing the injured Chekov from a hospital, saying that it might not be logical, but it's the right thing to do.
 * 6) Kirk's attempts to use profanity (or "colorful metaphors" as Spock calls them) end up going hilariously wrong, including when he reacts to being called a "dumbass" by saying "well, a double dumbass on you!"
 * 7) One of the film's most famous scenes features Spock nerve-pinching a punk on a bus when he refuses to turn down the music he's playing at an obnoxiously loud volume.
 * 8) The scene with Chekov asking a police officer where he can find some "nuclear Wessels" is often considered the single funniest scene in the entire Star Trek franchise. The later bit with him being interrogated by two US Navy officers is also very funny.
 * 9) Nice bit with Scotty trying to figure out how to use a then-new Macintosh computer.
 * 10) Awesome scene late on, where the Bird-of-Prey decloaks above a whaler that was attempting to harpoon the two whales they intend to bring back to the 23rd century.
 * 11) Impressive special effects
 * 12) Like the previous film, it shows the crew dealing with the consequences of their actions in a realistic way, and the threat of them having to return home and face treason charges makes a nice contrast to the overall lighter storyline.
 * 13) Great ending, which comes at some personal cost to Kirk (who is demoted from admiral to captain), but sees him and the crew rewarded for saving the Earth by being given the new USS Enterprise-A.

Bad Qualities

 * 1) Many of the film's jokes are heavily rooted in 1980s pop culture, and may go over the heads of younger viewers.
 * 2) It's never explained exactly what the probe is, or why it wants to talk to humpback whales.
 * 3) The soundtrack can get a little corny at times.
 * 4) At one point the film showcases a needlessly gory video of a whale carcass being dismembered, something which slaps the viewer with its "Save the Whales" message a little too hard.