every engine used for rendering (most common - DAZ, HS/HS2, Koikatsu, VAM, TK17) have huge variation in quality depending on many factors - assets used, lighting settings, additional visual and processing effects, and so on...
Koikatsu, what this VN uses, is no exception to the rule and considered this huge variation - i wouldn't say most games are nothing like this, because they are all over the place, including those looking close enough visually, here are just few examples -
Dissonance,
Another World,
Unto Starlight