Almost everything in this manga--the characters, their economic situations, their hopes and disappointments, and above all their smoldering feelings--is very much like stuff that has happened to me or people I've known. Some of this realism is actually painful to watch, particularly the long, passive avoidance by the main character of the good things reality is offering him. Nevertheless, that's the way people, in fact, often are!
And the other characters in this manga, who are mostly less irritating than the MC, make up for his unwillingness to move on by being especially likable and interesting. Toume Kei is a woman, and maybe that's one reason why her female characters tend to be so deep and interesting. Or maybe not--but in any case a story with such interesting women in it is, perhaps paradoxically, bound to be of extra interest to male readers. And I believe that most female readers will like this manga simply because they will probably be able to thoroughly identify with it.
In short, it's a very well-told story about romantic uncertainty playing out in the lives of people in their early 20s. That's one of the great themes of story-telling, and this is a very good story of that sort.
And please note this is a story of JAPANESE people, who generally are expected to live up to high standards of work, decency, and loyalty, and are especially expected not to have sex with anyone but the One they finally find they'd like to spend their whole life with. This is the story of people growing up into this society and its expectations. That's bound to be quite a struggle!