great story + well integrated ero scene in the story + gameplay = best sell
I wouldn't take ero into the equation at all times - while I'd probably agree that the best VNs should have a great story, I can't agree that the best VNs must include sex. There can be stories that don't focus on relationships - you can have a gripping political thriller where sex wouldn't be of interest to the story at all. So maybe "if needed, well integrated ero scene in the story
Bad story + 0 eroge scenes = bad game
Bad story + eroge scenes = medium eroge game
Great story + 0 eroge scenes = great game
Great story + eroge scenes = best game (Like Tsukihime for example)
About classification, I would distinguish between "game" and "ero game". You can have a
- bad, medium, great and best game
(with this, a VN in general is probably meant), and you also can have a
- bad, medium, great and best ero (sex) game
So the components and outcomes of the equations aren't really logical. What those 4 equations do tell is that you are a fan of well-placed ero scenes.
This is for a dedicated topic, and it's a very debatable subject, but if you needed to identify components by which to judge certain game categories, the standard equation (more or less the outline of a typical review) would look like this:
- story + art + audio + direction = (bad, medium, great, best) game
As I said, it's debatable anyway, and you'd want to throw in timing, audience, genre (here we could have "ren'ai" or perhaps "sex" in the genre-way), vision, expectations, and a million other things that aren't quantifiable in the first place.
EDIT: Ugh, I hope this doesn't sound aggressive, I'm just really very much into structured things. And it's 2:30 a.m.