This is the story of a spy pretending to live a normal life: it's not a serious tragedy, it definitively falls under the comedy genre but at the same time it has many serious aspects that make it very interesting.
First of all, the characters are all very likeable and their family life is the main reason why this manga is so attractive. It's cute, it's funny and it keeps you concerned about the fate of our protagonists, although as of now I feel like the wife is getting much less screen time than the father and daughter.
It has a nice touch of humaneness in it, using a protagonist that appears insensible at first but all of his actions are very kind, and his motives are understandable. Why he does his job, why he's that way… all of it makes sense, ultimately, and his aim for peace is very credible.
But adding to this slice of life / comedy aspect, the novel is set in a replica of the Western Bloc of Germany during the cold war, and I believe the author did an extremely nice job in this case. He's not trying to show an ideal world of happiness, but he's not painting a world of horror either, I think he got the atmosphere right and you find a perfect setting for spies and conspiracies, with a neutral depiction of an autocracy. Didn't people ultimately live, at those times too?
It's nice to see that the author is also willing to break a few taboos, such as people dying or main characters killing. There's no sweetener about that, the people we follow here might do cruel things and there'll be neither justification nor condemning.