How is a visual novel not a game? You have input, upon input something happens.
I understand it has none of the usual core factors you try to evaluate, but instead you can focus on style, pacing, different choices - do they matter? do they give flavour text or nothing at all?
Are the characters realistic? Likeable?
Edit: Sorry .. I missed the negative if .. welps. orz
Still, does it offer no dialogue choices at all? Or do they simply have no impact?