Video game characters attempting sincerity tends to not work out. Frankly speaking: Most games that make an attempt at sincerity fail.
There are exceptions of course — Joel and Ellie from "The Last of Us" come to mind — but those are exceptions, not the rule. "God of War," unbelievably," nails it.
The game's main characters, Kratos and Atreus, are entirely believable as a father-son duo. As the duo grieve the death of the family matriarch — Kratos' wife / Atreus' mother — they have to reckon with each other.
Kratos, as he's known to be, is a relentless dour, embittered man. He hates the Gods, expects nothing from life, and is always serious. He offers life lessons like, "If you never expect anything, you'll never be disappointed."
This is his resting facial expression:
That tone is delightfully contrasted by Atreus, who's excited to explore a world he's never seen before.
He's fascinated by history, impressed by the amazing things he's seeing, and excited to talk about it all (much to the chagrin of his angry dad). In this way, Atreus stands in for the player — impressed and excited rather than over it — while Kratos is putting on his usual stiff upper lip.
He's also a realistic depiction of an adolescent boy. He asks his father for reassurance often, overplays his own abilities, and is generally excited for adventure. He's clearly trying to find himself while asserting his own maturity. He's awkward, just like so many pre-teen boys, and grumpy, and isolated, all on top of the fact that he's grieving the death of his mother. Atreus' growth throughout the game is a joy to watch.
And that's before we start talking about the game's other central characters, each of which is surprisingly fleshed out and integral to the story. But you should discover them yourself rather than have me spoil them.