In most of the episodes, he doesn't have that large of a role: he comes by, mentions something about the mushi that somehow affect the people he encounters, and then things take their course. As such, the series is much more a commentary on the human condition, with all of the emotions that humans can have, than it is about the mushi. This was also apparent in the first series, but since all the exposition has already been done, the second series can focus on the humans instead of the mushi.
Again, the character art is simple but effective. But the backgrounds are really beautiful. Dramatic things are shown, not told, in poetic visuals. Together with the low key music, the series paints very intimate portraits of the people featured in the show.
The first series is a must-see. The second series perhaps even more so.