Really excellent game, I love it, for very specific reasons :
1) The 3D: it's the only game I know of this sort (there may be others I don't know about), and the way it enables to view the sex scenes from all angles is just.really.great. It enables to feel part of it as no 2D games can.
2) (and maybe I should have put it in the first place) I love the MC: he is confident, but also so tender, so sweet, "so cute" as the women of his life often say, and at other times so selfish and careless; he is a complex character who makes me really feel for him, something that rarely ever happens with other game characters.
3) The relationship between the MC and his mother: this goes with 2) above, but this is the most tender relationship, and the most passionate, so for me, the most likeable; again it makes me feel for them, and imo, making a player feel for a porn game character or relationship is quite an achievement!
4) Unlike some others, I like the point system; I like the slow progression and the fact that you don't really know what you should do next to move the story forward: it makes you explore and brings wonderful surprises when suddenly, the situation does evolve!
5) The face expressions; I think that most of the characters' faces (including the MC's) are between plain and ugly (to the exception of the teacher), but very expressive (particularly the MC) - which most certainly partly explains 2) above.
6) (the result of 1 to 5; hum... maybe excluding 4...) It's like no other game (that I know of), where a lot of other games look alike (some much better than others, some really great, but still in the same genre)
Now, what criticism could I make? I guess the main one is that you can still have scenes that do not make sense anymore once the story evolves - the dialogues of thoses scenes should be modified depending on where you stand - but I guess this would make the coding (or whatever technical term goes here) that much more complicated. Oh, and conversely, sometimes you can see a scene that you should not be able to see yet, because you did not trigger a specific event that explains such scene. And it is definitely grindy... I like grindy, but there is such a thing as too much grindy...ness(?), right ?
Anyway, to sum it up in a nutshell: great game!