When Star Trek went to the big screen in 1979, audiences were excited, but Star Trek: The Motion Picture was too long and slowly-paced to stand the test of time. It was also extremely expensive, causing Paramount to rethink making a sequel. So changes were made: Gene Roddenberry was fired, a budget-conscious director was brought in, and the script for The Wrath of Khan was written by a writer who'd never seen a Star Trek episode. The production staff not only learned from the mistakes of the first movie, but used the existing sets and unused footage to save money. The changes had repercussions beyond Star Trek.
The cumbersome large model on wires approach was shelved for Star Trek’s motion control, and new models were built with usability and cost in mind, rather than screen presence. The only thing not cut back on was the aforementioned CGI. The large terraforming sequence could only be done in animation, and much like the sequence in the finished film it was presented as an advert for the skills of Lucasfilm Computer Imaging. And like in the film, the CGI video succeeded in its marketing purpose. The clip impressed a young Steve Jobs enough to part with $5 million to buy out the division, which renamed itself Pixar.
But what really made the The Wrath of Khan a hit was a plot that focused on the original cast and a villain that harked back to the TV series (to be fair, V'ger did, too, but not as charismatically as Khan). Read about the process of bringing The Wrath of Khan to theaters at Den of Geek.