This manga was incredibly sad and depressing. It does a good job at having the reader sympathize with Ooba, which is quite difficult due to the fact that by all account he could be considered a terrible person. Still, it is often the people that are seen as terrible, the good for nothings, that have the worst things happen to them and hence by making such a character one that can be sympathized with the story ends up tremendously depressing. In most of these cases, even if there are external stimuli, the cause of Ooba's despair and depression is usually Ooba himself, and his peculiar way to dealing with the world. He finds chances for happiness again, and again, and again, being set up for success at every opportunity, but he manages to screw each and every one of these up due to his own actions, but in ways that made sense considering who he was, wherein even if the reader could see that what they were doing was completely wrong and would inevitably lead to ruin, that it made sense why they would proceed like that. And in the end, that's what makes it most distressing, in that this isn't some story of someone dumb or someone with terrible luck, but of someone incredibly lucky and intelligent for whom things still end up completely falling apart around. The art is also good in that it is able to seem normal and good looking when necessary, but also feel incredibly dreary when such an atmosphere is called for. 

tl;dr: The tale of someone who fails at life told incredibly well and thus being immensely depressing.