It's definitely a comedy, and definitely, while on the surface light actually is pretty dark.
Each "arc" of the show is more or less totally separate from each of the other ones, though I think a pretty good job was done with jumping around the different arcs (iirc, the light novels were not written in the order that the anime was).
Personally, I find the theme of the show to be exactly what the title implies it to be -- the decline of humanity. In general, each arc will begin with an episode that takes a look at some quality of humanity, or introduces some archetype of humanity, then is generally followed by an episode of total downfall.
At the end of each arc there is no longer any surprise as to exactly why in this setting, humanity has declined. Yet there is a certain sweetness to once was; and so while one might find the antics of the characters to be foolish, you can't really help but smile in sweet nostalgia while you think : "something like this happened to me once".
9/10 -- I'd like to give it a 10, and while I find the weirdness and caricaturization to be part of jintai's charm, at times I also find the show to be a little too weird.
