Star Trek Takes a Turn, for Better or for Worse: Star Trek IV

Summary

An alien ship sends out a signals that disrupts all energy from ships and even planet Earth.  They seek the whales that used to live on Earth, now extinct.  Seemingly, the situation on Earth looks grim.

Meanwhile, in the last film, the Enterprise crew--rather the officers--have stolen the Enterprise and crashed it to rescue Spock.  So they are to be put on trial upon their return.  As they fly near in a Klingon ship, they spot the bad situation on Earth and decide to help out.  They decide to make the ship go back in time be exceeding the speed of light by so much, which Spock has sort-of calculated, and capture a few whales to bring back.

Commentary with Spoilers

As the movie unfolded, I mistakenly assumed it had not done well.  (It was both well received and did well at the box office.)  Unlike the first and second movies where scenes stuck in my memory, nothing about the fourth one stayed with me except that it dealt with whales.

Positives

1. Light-hearted humor -- The crew while engaged in the story, never quite see their mission in dire straits, but rather seem to accept it as a field trip.  The actors appear to enjoy this change-up.  The best scene, which may be in this trailer, is when Spock and Kirk are invited to dinner.  Spock says no, he's not interested.  Kirk says yes.  Repeat.  Very simple, very effective--Spock's straight face, Kirk's small wry smile.  These two had great chemistry that has yet to manifest in the latest series.  Perhaps Shatner and Nimoy had so many years to perfect it:  Nimoy's straight-laced intelligence and Shatner's loose-cannon gut-genius that contrast so nicely and yet they admire one another.
2. Present day (well, the 1980s) dissected -- The crew take a few jabs at then-current culture.
3. A nice switch-up in subject matter -- not about death and war but endangered whales.
4. Series consistency -- The original series had much variety, so this change of pace--humor, different subject matter--was a welcome reprieve.
5. Continuation of a larger story -- There's a larger story arc beginning with movies number two and three, that wraps up in this movie, tying them together, perhaps giving the series a more epic feel. 

Negatives

1. Light-hearted humor -- Chekhov is caught aboard a Navy vessel supposedly near a nuclear reactor.  He tries to stun his interrogator but fails, so he flees, chased by dozens of men with guns.  He falls two stories and goes into a coma.  The comic background music tells the audience not to take this seriously.  [See below.]
2. Time travel -- Spock's sort-of calculating is quite accurate, and problematic:  Why hasn't everyone been time traveling up to now, causing all sorts of havoc?   
3. Drama -- Nothing and no one feel like they are in serious jeopardy.  Part of it's the comedy, but part is that they too quickly rescue any bad scenarios.  They don't push the tension.  Maybe it was meant as a children's movie, which would explain much of the film.
4. Theme -- It touches on a lot of things but isn't able to develop anything with much depth.  Is it a critique of the 80s?  an examination of our attitude toward the plight of other creatures on our planet? a reminder that it's okay to steal and destroy as long as you save whales?
5. Characters and scenes -- Nothing stands out.

This is a necessary addition to the series, adding variety, showing a new face of the Star Trek crew, but a few items required more thought.