Aye, we've had this discussion in the past.
The only two movies that seemed to break the rule of Star Trek films being action-adventure were Star Trek TMP and Star Trek IV: The Voyage Home.
While TMP was a financial success, it was far from a critical or even popular success. (Although it still remains among my favorites in the film franchise...and, as a side benefit, I find it to be an excellent sleep aid, which does not bespeak a lack of quality, but simply its serenity).
But yes, for the most part, the Star Trek films have largely become action adventure...and the JJ movies even moreso. Insurrection and Final Frontier failed to succeed largely because they took place on planets that the viewer didn't give two damns about. If Earth wasn't endangered or somehow involved, then the audience just didn't care. (Which is another thing that forces Trek to become crippled. The Wrath of Khan seemed to be the only film that managed to sidestep the whole "Earth is in danger" stigma and pull up a successful box office (for its time). That, and for the TNG films, First Contact.
Star Trek TMP ... Earth is endangered by alien probe seeking only to find its creator and join with it.
-Strengths: Excellent visual effects. Definitely showed the leap from small screen to big screen. A good, if heavy handed story. Return of our favorite characters, a new view of the Klingons, and the introduction of some new (if short lived) characters.
-Weaknesses: Supposedly wooden acting. (I just didn't see that at all. I thought the characters were spot on...redeveloping for the new medium they undertook...the big screen.) Lots of flying over country in terms of the long, long trek they took through V'ger's energy field just to reach the ship at the heart of the cloud.
Star Trek II: The Wrath of Khan-- Earth is not endangered, except maybe only by extension if Khan is allowed to carry out his plans with a powerful Federation starship and a powerful, planet altering/creating device at his disposal.
-Pros: Again, excellent visual effects, and the budget (much smaller than TMP's) which went toward them, thanks to an ingenious use of stock footage. The interpersonal stories for Kirk and Spock, and McCoy to a degree. The original series always excelled in this area, and it showed in this film. The acting was solid, although I still find Kirk's "KHAANNNNNN!!! KHAAANNNNN!" to be rather ham-fisted. Loved the cat and mouse nature of the space battles...the strategic elements, and the lumbersome nature of two capital ships fighting each other (something I honestly have not seen replicated in any of the Trek films that followed).
-Khans: I'd be hard pressed to find any, except that we never really saw Khan in action like we did in Space Seed, and later on in Into Darkness. Other than that, this is the original series' crew's most solid film, aside from The Undiscovered Country.
Star Trek III: The Search for Spock. Earth is not exactly in direct danger again, but it is in an implied state of danger if the Klingons manage to get a hold of the Genesis information to create a weaponized version of the device.
-Strengths: Beautiful story of loyalty, honor, courage, and sacrifice, much like its predecessor. We gain more insight into the Klingons, thanks to excellent performances by two actors generally known for their comedic prowess in other circles.
-Weaknesses: Visual effects were serviceable, but nothing really special...except maybe for Enterprise's demise. This movie seemed to look cheaper than the Wrath of Khan.
Star Trek IV: The Voyage Home. Earth is implicitly endangered by yet another probe, this time, searching for what happened to Earth's whales.
-Strengths: Light hearted adventure, taking place largely on Earth in its past, creating the inevitably hilarious "fish out of water" tale for the crew. Decent visual effects, and an interesting time travel sequence.
-Weaknesses: Again, I'd be hard pressed (as with Wrath of Khan) to find any weaknesses in this movie. I would say, if there was any weakness to this film, it would lay in the score by Leonard Rosenman. (Up until the excellent score of The Undiscovered Country by Cliff Eidelman, I would've still preferred the works of Goldsmith or Horner.)
Star Trek V: The Final Frontier. No danger to Earth at all in this film. There is a price on Kirk's head that Klingon Captain Klaa wants to collect, but unfortunately, it is downplayed by the forced comedic nature of this film which tries to explore common spirituality between humans and more passionate Vulcans.
-Strengths: The film has some good dramatic moments. The "blast from the past" sequence with Kirk, McCoy, Spock, and Sybok was a nice touch.
One of the best lines in the film series: "What does God need with a starship?"
-Weaknesses: Visually, and story wise, easily the weakest of the original series films...looks extremely cheap compared to even The Search for Spock, and the humor, as stated before, seemed forced, trying to capitalize on the more innocuous nature of humor in the previous film.
Star Trek VI: The Undiscovered Country. My personal favorite of the original series films. Again, Earth is not endangered directly, but indirectly if conservative Klingon forces decide against the peace initiative started between Captain Spock and Chancellor Gorkon.
-Strengths: Improvement on visual effects over the last two films. Excellent acting as always from the cast, and I enjoyed Christopher Plummer as General Chang. A good "end of the Cold War" allegory, and a fitting end for the crew of the starship Enterprise in the TOS era. I think it would've been interesting to actually have seen Saavik be the traitor to the Federation, instead of inventing a new, sexy Vulcan female to have to take the fall. (Of course, that would've rubbed fanboys the wrong way, and we can't go around incensing fanboys now, can we?
) The return of the K't'inga class battlecruiser to the big screen after 12 years of neglect, (sorry, but stock footage from TMP for a simulation in TWoK does NOT count
) although I would've loved to see it in battle.
-Weaknesses: Over-reliance on the Klingon bird of prey as the main bad guy ship, as with Star Trek III and V. I sorely wanted the K't'inga class battlecruiser to be the ship that the Enterprise and Excelsior fought. The photon torpedoes looked really generic in this otherwise visually gorgeous film.
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