LOL. I don't have any personal reason for so called "butter". The "Marvelous" judgment came from that I've play many 3D games, and Milky Way looks very professional. It looks realistic, don't have any glitches (in public editions), good mechanic and story.
In my opinion judging only by photos below the post is a mistake towards the overall graphics in those case - attached photo don't give you opportunity to feel free rotate camera, and 3D free-to-explore word.
I know it varies from player to player that "what is most important in porn games". The one who says "the graphic" will hardly any consider to play html games like for ex.
The Claim(gg btw), because the graphic content on those are mostly limited to pictures, witch cannot be compared to 3D content nohow.
Currently, I'm guessing that graphic is most demanding part of creating the game if we look strictly at technical side - there is no problem to type a scenario into the game (frankly it demands only a typing), but it could be a huge problem to draw even one picture for a renpy game, if you lack of knowledge on drawing program (not mentioning DAZ, Unity3D and other).
TL;DR: Don't base your judgement only because on game screenshots. Play it.