-Solid 5 for me, the art and animation is phenomenal. One of the best i've ever seen. Unlike some poorly made animated hentai, which just includes a picture of a dick move in and out of a static pussy, in this game, the artist nailed the feel, each thrust, each bounch, you will feel the weight of the characters. So even though the control are just simple motion ajustments, this's still really good to fap to.
-I said 5 but only give 4 because i think the game is held back really hard by the gameplay. Is it repetitive? Of course it is, i don't expect they made a deep story with unique scenarios each days. But the problem is, look at what monochrome sister (whatever it's called) did, it had many thing to distract you from its repetitiveness. Like going out with your sis, buying food, decide who is cooking. This game has only 4 options, talks - reading repetitive texts, flirting - reading repetitve texts, bath - reading repetitive texts, sleeping - reading repetitve texts. I think that's the problem, no diversity in the gameplay. They could've made like watch tv together, reading together serving the same purpose as talking. Workout, cook, clean up together serving the same purpose as flirting, etc.
-About story, i think you should read other reviews, they are more well versed in this aspect. But i assure you that the NTR part will not meet up true NTR fan's standards. It's just the same stupid shit you see everywhere on nHentai, somehow the girl become really stupid under some stupid circumstances cliche. Generic as it gets so don't expect much.
-In conclusion, i think this is 5 point fapping potential but 2, 3 point co-habitat game potential, 2 as a Ntr game
-Edit: I love that they let you choose which kind of sister sprite you like, a submissive (idk if this is the right word) one or a confident one. Crossing finger that they will update a loli one, no?