Looked past the graphics and gave it a shot, it's actually fairly decent/borderline good. I really really appreciate games that have animated sex scenes and that will skew my review. The worst part of my experience in playing was the grind to get to the sex scenes, however that could have just been me being a dumbass. The "story" takes place over 30 days (but let's you go on after if you don't make it by then - BRILLIANT FEATURE), however I did not get a sex scene until day ~70 or so. Due to this I imagine I am just a dumbass. That said, it did take me a few hours to get to sex content so if you are looking for a quick game, look elsewhere.
I'm not sure if I have gone through all the sexual content yet or no, but what I have seen has been great. A decent amount of variety (positions, areas), a good theme (slowly seducing/corrupting your step sister into your "whatever you want her to be"). Animation is better than the graphics, but graphics honestly aren't terrible imo. If it weren't for the grind early on, this would have been 5 stars from me, however some people may be off put by the Engrish (it's understandable but the author/translator is definitely not fluent).
All in all, I think it's worth a shot if you are at least mildly curious.
Edit: changed to 5 stars to off set the recent 1 star review xD "unplayable" haha, I probably put ~15 hours into this game. I think that is a classic PEBCAC error.