Kiss x Sis strangely enough is one of the better romance stories I've read up to date. The writer definitely knows how to keep the manga going, throwing twists, changes, character development and even different writing focuses throughout it's runtime. And I have to give him props for that. It's almost never nowadays that I don't have the feeling that the story is dragging it's idea out for way too long.

[Quick sidenote, the title is probably top contender for the most "technically true" titles. Sure it does happen, even more than a hundred chapters in, but it really has stopped being the focus about 20% of the way in, it's not a gag manga.]

Now, if you start reading, you will definitely feel like an 8 or 9 is off. I was at first confused too, it felt like just slightly spicy ecchi, could just spend my time reading a hentai instead. If it kept that way I might've given it a 6 or 7, nice art, cute waifu's but not really much else.

But then something weird happens, quite quickly even. It's definitely the first time I've seen a manga do this.
Now just to give context, this has a harem tag, to be specific, it has 5 members (not gonna tell which though, since it would be a minor spoiler)
So what happens basically, it's that a side character becomes the main character, and the main characters become less important than the new main, but a bit more important than the other two.

this happens I would guess about 4 times total for now, some being much more satisfying than others. Like the comedy between ch40-80 absolutely killed me at times. And the more new self deprecating main character actually got me liking him more than back when he was full dt mode (like is usual to harem mc's)

Also, not to worry, at first it was just a somewhat more daring ecchi but the new chapters definitely has it in full smut territory (the territory where sexual acts are shown but only a few panels instead of a full focus on it like a hentai)

And really, to be honest after a while it becomes rather hard to dislike the cast, sometimes the changes in them are a bit strange, but overall it feels like they actually could be people (unlike the earlier chapters) and that they're actually growing at the rate they're aging in. Which is probably a thing you don't see too often from Japanese media, characters properly acting their age.

Overall it's great stuff if you want to be entertained, quite a bit of the focus is on the perverted parts but it has quite a bit more to often. If you're a guy definite recommend.