There was way too much in-yo-face sex, which the main character did not have to earn in any way. This is a big turn off, makes the women seem one dimensional and stupid, breaking immersion because you painfully realize you're just in some other dude's stupid 3D fantasy which is feeding you with pre-planned (by him) empty sugar-highs.
The renders in the game are cool though, I played a fair amount of it before simply getting too bored to even load up my own save, because when you look at the save/load screen all I see is all the pointless fucks that have happened to our main character so far, and none of them mean anything to me because it was all "on rails" and required no participation from me.
Typical of this game are empty choices like: "Fuck your sister's girlfriend? Yes/No"
But no matter which you chose, there's no point to it. In a better designed game, this same choice would have been a branch in a bigger tree where you try to find how exactly to fuck your sister's girlfriend, and possibly how to not fuck up your chances with the sister while doing so.... But nah, in "Sisterly Lust" it's always just a simple and pointless "Yes/No".
The renders are good though and maybe you can look beyond the shortcomings of the story and gameplay, just treat it as a series of porn pics. It's not bad if you consider it as a set of porn pics, so I rated it average.