The truth is that Rogue One commits the same sin as most modern action movies: there is too much action.But this isn't to pick on that blog, you've probably had similar conversations with your friends.
As a result, you can't really tell much about the characters, as they spent 95% of their time being shot at, shooting people, or running away from stuff. The characters certainly seemed serviceable enough, though I don't really remember their names or much about them.
But this ignores that in an action movie, the action is the characterization. Part of what has made Star Wars so memorable hasn't been intricate monologues and flackbacks of backstory or other humanist fare, but rather extremely good and brief archetypes. Boba Fett is the epitome of this, but really you have Lando, Palpatine (in the OT), Tarkin, Greedo, Ewoks, Admiral Akbar, Wedge Antilles, General Grievous, Mace Windu, Boss Nash, even Jabba the Hutt. None of these are characters with a "rich backstory" but their character design and costume and appearance gave us a bright image that could stick with us. We don't know Boba Fett's internality, we just know that he is really cool.
Rogue One does this with the entire cast. It plays to Star Wars' strengths.
As proof of concept, I'm going to list what we know about these "shallow" characters, just from the brief action they get.
- Bhodi Rook (the Pilot): This is the prime example. What we know about him, visible in every action scene but never a word spent on, is that he is a coward. Not a moral coward, but someone genuinely afraid of physical violence and dangerous situations. He tries to bluff his way through them, then he stammers and sweats and doesn't know what to do. (The brain eating slug scene does dual work for showing Saw Gerrera's obsessive delusions, trying to buy safety in the form of an alien creature, and the trauma Rook suffers that makes him understandably afraid of violence.) He is a broken man. And that is the difference between "not having fear" and "bravery" - he has fear but he overcomes it. He defects to the resistance with key information at great cost to himself because it's the right thing to do. He risks his life to send a signal to the fleet in a scene that would be effortless for a normal hero, but is genuinely costly for him.
- Saw Gerrera (the Guerilla): If Mon Mothma and Director Krennik are imagery-mirrors of each other, Saw is a mirror of Darth Vader. Both are played by black stars (and if human racism is central in Star Wars, white racism is still very much a thing.) Both have these eerie breathing apparatuses. They appear in this half-mechanical, dark looking figure. Vader is an unrelenting extremist for the Empire who gets things done, even if it means disposing of ineffective underlings. Saw is just that, but for the Rebellion.
- Cassian Andor (the Intelligence Officer): He gets more dialogue to explain his internality than most, but I'm just pointing out how they use his first scene, where he shoots his own informant, to symbolically backstory his guilt about "all the terrible things I've done" that leads to his final mission.
- Chirrut Imwe (the Monk): He is simply put, a Force-worshipper without Jedi superpowers. This concept is enough to make him interesting and not really require more explanation. But we get more! We don't see him as a holy monk, but as basically a street beggar, like running into Falun Gong in Times Square. He's haunting this desecrated temple of the Jedi, leaving us to ask why? Does he have nowhere else to go, does he hope to meet other worshippers there, is he trying to protect what he can? He acts very confident that the Force will guide him, but in action he relies on his non-believer friend always being there to back him up. "I don't need luck, I have you!" And yet Star Wars has long defined the non-Dark Side Force as "your faith in your friends is (not) misguided."
- The Erso Family: There's this post about Galen, and this one about Jyn's fathers, but even her mother Lyra has characterization. She's some sort of zealout Force-worshipper that convinced her more moderate husband to move away from the Core and run away to the green place where they wouldn't be responsible for turning Jedi Kyber crystals into deadly weapons. And when the chips are down, she is dedicated enough to go on a suicide run against Krennik. That's half the personality her daughter inherited.
- And I really can't get enough of Jyn's relationships with guns. She was resentful that Saw left her with just a gun when he abandoned her. She used the skills Saw taught her to steal a gun while at Rebel HQ and that provides her with a smidgen of independence. And her most honorable moment is when she gives K-2SO a gun as she abandons him, which he finds deep meaning from (and it's so delightful how she does it with her same little passive-aggressiveness she displays whenever she is nervous.) Guns are complicated symbols in Star Wars of course, because of they will never be as good as / as cool as / as civilized as the laser sword.
- K-2SO is great and I don't think anyone's complained about his characterization, which is almost entirely done through one liners and appearance jokes with other Imperial Droids.
- Who in the comments wants to tell me what they know just from the actions of Baze Malbus (the Heavy)?