Action movies with good plots start with a compelling character, a protagonist you can root for.
To “Root for” the hero doesn’t mean you like them. Anti-heroes can be despised. Wicked men can still be the main characters of the story.
For example, Ebenezer Scrooge is a bad guy. But you are rooting for him, insofar as you are looking for the chance at redemption: can this man change? In the same way, any character can be compelling. Just give them enough motivation, aspiration, and meaning.
There are two main ways we see compelling characters presented in a good movie plot. They are set apart, and they experience pain and exhibit flaws.
Set Apart
When a protagonist is set apart, they have a uniqueness to them compared to the characters and world around them. This can be some sort of special power or unique skill set that makes this person different for their world. They are in a position which calls on them to take on the adventure.
Anything from superhuman powers like “the Incredible Hulk” to more exceptional but reasonable skills, like Hawkeye’s amazing skills with the bow. Note that with Hawkeye, his skill appears to be technically attainable, but incredibly unlikely for almost anyone to achieve.
But this “set apartness” doesn’t have to be some tangible skill or sci fi super power. For example, Frodo from the Lord of the Rings isn’t exceptionally skilled, but he is known for his stout heart and resilience, which becomes critical to fighting the temptation of the ring as he continues to carry out his task to bring the ring to Mordor.
Pain & Flaws
In order for us to best care, we have to be able to empathize, or even better, sympathize with them. The best way to do this is to be able to identify with them through experience.
Pain: A common start to a protagonist is some form of early loss, such as the death of a family member, (see examples like the parents of Harry Potter). Or are they are enslaved? Lost a limb in the war?
Jake Sully in Avatar is a great example of a character who was set up well, where he cannot use his legs (unfortunately, they did not use this origin to its full potential). This sort of disastrous pain and frustration should continue to happen throughout the story. But it occuring at the beginning is a great way to create empathy.
Flaws: if they are perfect, it is hard to identify with them. When they have character flaws, we relate to that pain.
Do they have a gambling addiction? Feel socially insecure? Regularly aggressive and rude in conversation? All of these are flaws which, while we may or may not have them, are understandable and unfortunate to see.
Frodo doubts his friends. Pippin is clumsy. Dr. Bruce Banner hates himself and thinks he is a beast. Dominick Cobb in Inception blames himself for the death of his wife and it haunts him throughout the movie.
This leads to a secret flaws. Flaws are often secret, with hints of those problems or flaws hidden behind other flaws.
This extra layer adds depth to characters. It makes them more believable, because most people do not say exactly what they are thinking. We misdirect or hold the truth back due to our flaws or insecurity. Great protagonists act the same way.
Integration is Critical
Pain, flaws, powers and unique character traits must not simply be present. They must be integrated into who the character is and what they do in the story.
Jake Sully started with a great pain, but when he ignores his pain and acts like his pain means nothing, then his pain is not integrated into his struggle throughout the story of Avatar. The audience does not care that he cannot use his legs because it does not affect him or the story in any notable way.
Compare this to the incredible Hulk, who’s power is also his weakness, a rage he struggles to keep in control. In addition, it is his creation as the Hulk which causes the military to chase after him.
How Modern Movies Fail
In Ant Man and the Wasp: Quantumania, Scott Lang’s daughter Cassie fits a mold of recent teenage marvel girls. She is a rebellious genius who can do quantum physics in her basement. She creates never before seen technology, clearly has problems with her dad, and wants to do the right thing.
That was all there was to her as a character. She does not develop from that starting point, and she is not forced to struggle in any way which impacts how she acts.
Another recent example is Thor Love and Thunder. Jane Foster does not really fit the character of a Thor. Her dialogue and actions show a take-charge attitude.
Jane Foster was a careful, methodical scientist in earlier movies. Becoming an action packed superhero violates the integrated character we have been introduced to before.
There are plenty more examples of the failure of modern heroes. For now, examine the movies you watch, and see if they pass the simple test: are the set apart, do they have pain and flaws, and have they integrated these into a cohesive hero? That's what makes a good plot, movies worth watching.