Most unique visual novel I've ever played, and forever a favorite. 

Probably the most interesting thing for me is that you're technically not the protagonist. You can't outright control her, you can only influence her. She ultimately makes the decisions, but you have to see if you can break or support her. The fact that you can choose to take completely different attitudes and relationships with her is great. 

This is so well thought out, and I don't think I'll come across a VN quite this extraordinary ever again.