(WARNING contains mild spoilers)
All of those television ads about "Captain America Civil War" calling it a superhero movie are lying (at least in my opinion). After seeing the movie this weekend, I can state for a fact that it's not a superhero movie - it's a political commentary about liberalism vs. conservatism which just happens to involve superheroes. The movie's plot deals the basic political debate Americans have been grappling over since 1776: big government vs personal freedom.
In the movie, the United Nations is preparing to pass the Sokovia Accords, which will establish an international governing body to oversee and control superheroes. The treaty, which is supported by an internationalist Secretary of State, would even force superheroes to reveal their secret identities to the government body, reminiscent of the the liberal call to reveal the names of donors to 501(c)(3) organizations.
The international body wants control over the superheroes because, sometimes, when they are saving the world, the Avengers' actions result in "collateral damage," the wounding and killing of civilians.
The Avengers, however, are divided about whether or not they should follow the accords. Tony Stark (Iron Man) supports oversight and signs the accords after being confronted by a woman whose son died because on an Avenger's action. Steve Rogers (Captain America) says he has more faith in his own judgment than the government's and wants to protect his friend Bucky from a government hit-squad, so he refuses to sign. Once a family, the Avengers become a family divided over politics (like my family during Thanksgiving dinner).
Another allusion to the political world today is the objection by many nations during the accord discussions that the Avengers, an America-based group fighting to save the world on their soil, don't first ask for permission. After all, national sovereignty implies that states should be able to make their own decisions on how to defend themselves against violence (even if the threat comes from extraterrestrial monsters).
The new Spider-Man is played much closer to the way the character is portrayed in the comic books---a young nerdy high school student. Of all the superhero characters in the movie, Spider-Man is the only millennial. And, just as in the case of the current campaign, when millennials tend to be attracted to the socialist policies of Bernie Sanders, in Civil War, Spider-Man joins up with the collectivism supporting the Iron Man side of the Avengers.
Even Black Panther character is reminiscent of politics today. While supporting the accords in the belief that superheroes shouldn't operate without being sent into action by the U.N., the Panther doesn't believe accords apply to him when he is looking to avenge the murder of his dad. This mimics the practice of most politicians of either party. It's called "do as I say and not as I do."
When Bucky is arrested, and later in the movie when much of Capitan America's team is arrested, they are imprisoned without access to an attorney in a secret underwater gulag which, some may say, reminds them of Gitmo. Of course, the big difference is that even though they are breaking the law by when they try to "do good," Team Cap is comprised of good guys, while Gitmo is a prison for terrorists.
In the end, as someone who has seen all of the Marvel superhero movies (not because I am an adult geek, but because I didn't want my son to have to go alone), I can say definitively that "Captain America Civil War" is the best Marvel superhero movie ever made (even through it's not a superhero movie).