With 1 being I hate it and 10 being I love it, I placed it at just 5, being okay.
First off, without me spoiling, those tags spoils a lot already. It is "borderline hentai"; however, for the anime, I personally think it is just plain hentai or soft-core hentai. I mean, the anime even had full blown censorship. As for the manga, I guess it is debatable on what is "borderline hentai". Someone told me it's ecchi but with many many many many more fan-services. I'm like sure. But what if it has full blown hentai scenes (just plain old sex scenes) but on a rarer occasion? Dun dun dun. Yeah, let's keep telling ourselves that.
Anyways, you still have your very hentai typical girlfriend who is cheating on you. But she redeems from her hentai-ness by having remorse and breaking up with the NTR dude. An actual hentai would have her stuck in a sex craze status unable to leave the NTR dude.
Take it however you want.
It was fun and interesting because it had the peeping hole twist that many others do not have. But I don't personally like this manga because the girlfriend cheats and he makes a huge fuss about it and blame her. He does the same thing and it's cool.
Call it spoiler if you want, I call it elaborating on the tags. Whoever invented tags just love spoiling anyways.
P.S. People said the manga is waaaaay better than the anime. It may be so for some. It probably is if you are looking for that mediocre plot. The anime is waaaaaay better as a flat out hentai. All the girls are even redrawn with the more generic anime character look instead of the unique yet odd style the manga uses.