Honestly, I was wondering why this was rated so high with the artwork not being that of I'd normally consider 'good enough' - this isn't a diss at devs that aren't capable of using DAZ nor are able to create nor hire artists that are able to produce really high quality art but having read a lot of R18 VNs on this site, I've become accustomed to a certain standard from highly rated projects.
Regardless, this isn't really relevant to Superhuman - in fact, I'd argue now that the art style is striking enough for it to stand out yet do not detract at all from the story and even enhance the mood for its reader.
Going back to the topic of the story however, not only is the game superbly written and presented - it manages to make me as a reader think 'this does not need R18 content at all'.
So, in short, I checked out this game because I was curious about how high quality of a smut this would be to deserve its rating - but came out of it thinking that the game's story can stand on its own without the smut. Granted, I do think that in the end the smut enhances the game as well - because, whilst life is good, it CAN be better.
Definite recommendation from me if you are even mildly curious about this game. The NTR tag is 100% avoidable for those faint of heart.