A proposed alternate subtitle: The Humiliation of Luke Skywalker.

Rating: 10/10 (12 December 2019)

There are two main ways to follow up a genre film. The first was perfectly encapsulated by Aliens in the "bigger is better" school. You expand the stakes, scale, and number of character to create a bigger, bolder experience. The second is to not go bigger, but to go deeper. The Empire Strikes Back might be the best example of that way to go.
The Empire Strikes Back actually feels a good bit smaller in scale than the original Star Wars. The biggest battle happens at the beginning of the film, involving a patch of icy land, several large walking tanks, and about a dozen speeders. That is smaller than the couple of dozen fighters attacking a moon sized base that can destroy a planet. The movie never goes bigger than that. In fact, the scale of the conflict continuously gets smaller as the film goes on.
At the beginning, the conflict is between the Empire and the Rebel Alliance. It's got galactic consequences, that great battle on the planet of Hoth. If the Rebel Alliance doesn't successfully get away, then the Empire's return strike after the destruction of the Death Star will wipe out its last major adversary for control of the galaxy. The next major set piece is the chase of the Millennium Falcon through the asteroid field. It's now one ship versus a handful of fighters and a Star Destroyer and the uncaring nature of outer space. It's a chase in order to capture the handful of occupants on board so that Darth Vader can lure Luke Skywalker.
The final conflict is between Darth Vader and Luke Skywalker. We're more than an hour since the Rebel Alliance has even been mentioned. The conflict involves only two people, not half a dozen. It's no longer about galactic consequences. Instead it's about a father and son and a conflict of good versus evil. The fight of the film narrows, and the only reason it can pull that off is because of the characters.
The original Star Wars utilized archetypes to tell its well-worn story. The Empire Strikes Back moves beyond the familiar hero's journey, and in order to accomplish that it needs to move beyond archetypes. Luke is no longer the farmboy hero. Instead he's an arrogant war hero who thinks far too much of himself. Han is no longer just the rogue, but a man with his own sense of right and wrong. Leia is no longer just the princess in need of help, she can push back on Han and control situations like she could only try to in the first. Darth Vader is no longer just the antagonist, he's now got a more complex goal of turning the hero to his side of the overall conflict. These characters are far more interesting in this second adventure than the first, and the story's structure of the second film is built to allow these characters to actually move through actions and change.
The center and highlight really is Luke. As I wrote a second ago, he's wildly arrogant at the start of this film. He goes out to check out a meteorite on his own and escapes from the clutches of a giant snow beast without help from anyone else. He also leads the successful feint against the incoming Empire attack on the Rebel base on Hoth, providing enough time for the transports to get away free and destroying a few of the AT-ATs as well. When he's sent to Dagobah to find Obi-wan's former master, Yoda, he thinks that he's beyond humility. He doesn't need it. He's awesome. But from the moment he lands on Dagobah, he fails at everything he does through the rest of the film. The capstone of his training is when he walks into the cave and fails to use the Force in the ways that Yoda had dictated, fighting the phantom version of Darth Vader and revealing that he had only defeated himself in the fight. He fails to raise his X-wing from the swamp. He fails to maintain control of his emotions when visions of Han and Leia suffering come to him. He fails to listen to Leia's explicit warnings of a trap. He fails in his fight against Darth Vader, only escaping through a desperate act of falling down a giant hole.
His constant stream of failures, capped by his failed confrontation with Darth Vader, humbles Luke. He no longer feels like he can face the evils of the universe alone. Dangling from the underbelly of Cloud City with only one hand, he calls out to Leia, desperate for any help. Even in the final moments of the film, he stands with his friends, not apart, and has become part of a plan to help the captured Han instead of running out there alone. Luke's journey in this film is fantastic all the more because it undermines the hero's journey he went through in the first. It goes against the idea of how we think hero's behave and succeed after their great victories.
It's the character work that really makes the film work, but the movie continues the first film's proud tradition of great design. There are expansions of the world in things like the Super Star Destroyer and the walking tanks the AT-ATs. Yoda is a creature come alive with puppetry. The fighters, the planets, and creatures are all great. The special effects move the technology of the first film forward, and it's always in the service of the great story and character journeys at the heart of the film.
Acting takes another step up as well. Moving directing duties from "Faster, more intense" George Lucas to Irvin Kershner was a surprisingly good choice overall, but it makes sense once you realize that The Empire Strike Back is more character film than science fiction adventure.
The Empire Strikes Back is a magnificent sequel that takes the characters from the preceding adventure seriously and gives them space to grow, propelling them through an adventure that truly tests them. It very rightly stands atop the world of genre fiction as one of the its greatest accomplishments.