I'll begin with a direct quote from a blogger who describes the manga's storytelling as Mono no Aware:

"Mono no Aware (in Japanese: 物の哀れ) is a sad nostalgic feeling that you get when you gain awareness that everything is impermanence. The realization that something beautiful is not going to last forever will intensify your appreciation towards that thing. It is the feeling that will make you realize how wonderful it is to come across such rare and fleeting existence."

Synopsis:
Not only Japan, but humanity in general, is entering a new era. Given the prevailing conditions, one can assume that there isn't much left to invent and research and the world is slowly winding down. These prevailing conditions are: A post-apocalyptic world marked by an environmental catastrophe. Androids that are barely distinguishable from humans. Nature that is reclaiming the once urban spaces of past civilizations. The challenges of acquiring and managing scarce resources such as coffee and fuel.

This is the world in which the characters of Yokohama Kaidashi Kikou operate.

However, this dramatic description is a stark contrast to how Yokohama and its characters present themselves to readers.

For a post-apocalyptic sci-fi story, this manga is uncharacteristically "boring." And that's a good thing. Let me explain.
Even if my synopsis isn't describing this as a happy world or place to live in, the characters are content with what they have. They show appreciation and gratitude to those around them and coexist with nature, while just living in the present and being okay with it.
Of course sometimes, the older characters rave about bygone days when they were still young. Or Alpha, an android girl and also the protagonist, awaits new letters from her departed owner, who has left "Café Alpha" up to her management, and whose return she longs for.
The way Hitoshi Ashinano depicts this world and characters, also depicts his love for nature, coffee, interpersonal and "mechanical" relationships, aeronautics, life in general, and maybe also cats (the facial features of the female characters begin to look more and more like these of cats at a certain point). I am assuming his love towards these things, but I am certain that if you are into slow reading you will love this manga!

In conclusion:
Yokohama Kaidashi Kikou is a very cozy slow paced manga with a melancholic setting and philosophical overtones – again, Mono no Aware fits it quite well. In some chapters, Ashinano-sensei omits text entirely to let his drawings do the talking, conveying the atmosphere of post-apocalyptic Yokohama to the readers.
I am very happy to have picked this manga up in its Deluxe Edition from Seven Seas Entertainment. It has a good amount of colored pages and the 2.5-times thicker size per Volume (compared to your average manga) is optimal in my opinion.

That's all.