People have varying opinions on this(like most things). Here's mine: this is not about a pedophile, this isn't about being a lolicon, this isn't promoting such things.
What it is about is a person whose life has ended up being rather sad and pathetic, and the escapism he turns to. While the guy can be disgusting, in my opinion, he often tries to do right but like in life, sometimes you screw things up badly.
This look at a sad life is what makes this a good manga. Its along the veins of NHk but further in that type of person's life. Give it a try, and then maybe it'll motivate some people to not end up like this a bit harder.
Except the ending is ultimately pessimistic, at the very end the character suddenly does a 180 and does something stupid that isn't explained, and despite not initially seeming like he did anything wrong, is taken as such(and apparently he meant it as such).
I've been thinking about this today and I decided to come back and explain why the ending is bad: Character motivation. In the end, the character makes a decision that has nothing to do with his character or his motivation and it throws the logic the manga has explained just to either give a very artificial bad ending or to stick it to otaku, except this character isn't one.
This man is somewhat respected at his job, he has friends, people that know him like him. Aside from what happens during the course of this manga, he doesn't live escaping reality, and this manga takes place under a relatively short time compared to his entire life. This guy isn't a man child otaku that collects figurines and watches anime, he isn't a pedophile that covets little children. He has a co-worker that he looks to as having a good life, this co-worker is just married with a family. His motivation is that he doesn't have much confidence and he wants very basic things. Once he starts to get them, he puts these things away.
I'm not saying he didn't deserve some punishment or to make a amends or even end up getting dumped, but the decision that causes these things was out of nowhere and doesn't match everything that's been built up. The lady randomly taking part at the end when she barely knows whats happening is a bit odd.