This manga had a terrible start but honestly, it's so much fun to read. The drama is well balanced with the comedy. The story is getting interesting. Unfortunately, it took me 60 chapters to start realizing that this might be a good manga. So... basically this manga just pulled a One Piece on me. It's definitely not one of its positives but what can we do.
I don't think it had a terrible start. In fact, I think it's been the way you describe from the beginning. It's just that, for one, the premise seems trashy at face value so one might not be inclined to take it seriously, and for two, it's taken an understandably long time for Koharu to adjust and thus for the dynamics of the hare-kon to settle and begin to improve. Taking 1/4th of the story to reach this point is par for the course when you consider the series is very much an earnest look at the hare-kon and the sort of people who'd get into one, including the inherent conflict and difficulties they face. Conflict is the fuel of a story, after all.
This manga is rather odd, when you think about it. It's a story about a subject that's generally a male wish-fulfillment smut fantasy published in a seinen magazine, but written by a woman from a female perspective like a josei. Throughout the comments section of each chapter and the general melancholic fascination with the drama unfolding, you see readers both annoyed at Koharu for not going along with being Ryuunosuke's wife given she chose this and he went well out of his way to help her, and readers understanding that she felt she had no choice, was in some regards coerced into the situation, and that Ryuunosuke has scummy narcissistic manchild tendencies. But I think they're both correct, and that the story has done a good job of showing why Koharu feels the (entirely normal) way she does, why she's having trouble adjusting even though she's just making her own life harder, and why she still feels the need to take accountability for the choices she's made, as well as telegraphing Ryuunosuke's good and reasonable qualities despite the apparently unfair way he's chosen to live.
It's an earnest shot at portraying how a woman would cope and even come to find happiness in this scenario and is a really balanced portrayal in that regard. The reader is often left feeling ambivalent like Koharu herself is, but that's really kind of the point. Granted, this is also probably the mangaka's fetish.