From the outside, Captain Metias definitely cuts an intimidating figure—he's handsome, serious, and very successful in the military. But that certainly doesn't mean that Metias is cold or unfeeling. When he's talking to his little sister, June, he reveals a side of himself that's extremely noble and thoughtful. He doesn't just blindly follow the Republic or think that poor people are disgusting—in fact, he chides June for saying bad things about poor people and experiences excruciating guilt when he's ordered to kill a little girl for escaping from her Trial.
This was what bothered him. I kept quiet and let him go on.
Metias ran a hand through his hair. "I shot a girl. She'd failed her Trial and tried to escape the stadium. Chian screamed at me to shoot her… and I listened." (2.10.95-96)
And it's this nobility that gets Metias killed. Instead of keeping his mouth shut and following orders (like a certain best friend of his), Metias decides that he cannot morally stand by and let the government continue to administer the plague to its citizens. He has to get out of the military right away. And that's why he ends up dead:
Straight through his intelligent, stupid, stubborn, overprotective heart. (1.4.84)
That would be a knife we're talking about here, folks. Metias gets a knife through his heart because he can't just swallow down his feelings of guilt over being a cog in the Republic's sinister machinery. At least he dies with a clear conscience.
Whereas the Republic definitely has a bad Big Brother complex, Metias happens to be the best big brother ever. He takes care of June as both a brother and as a surrogate parent—since both their parents are dead—and he's always there for her and puts her first, even when it gets in the way of his professional responsibilities. When June gets sick, Metias even skips his own induction ceremony in order to take care of her:
Metias ignored me and placed another cool towel on my head. "I'll be inducted either way," he said. He fed me a purple slice of orange. I remember watching him peel that orange for me; he cut one long, efficient line in the fruit's peel, then removed it all in one piece. (1.4.4)
It is through Metias's kind and loving example that June learns that even if they are serving the Republic, doing so isn't everything. There are things that are more important in life, like taking care of the people you love. That serving the Republic isn't everything only becomes clearer to June after she finds the secret notes Metias has left her, cluing his little sis in on the evil machinations of the government. Even after he dies, Metias cares for and guides his sister. Impressive, right?