This is a followup to @SorosFootSoldier@hexbear.net 's recent thread for completeness' sake.
I'll state an old classic that is seen as a genre defining game because it is: Myst. Yes, it redefined the genre... in ways I fucking hated and that the adventure game genre took decades to fully recover from. It was a pompous mess in its presentation and was the worst kind of "doing action does vague thing or nothing at all, where is your hint book" puzzle gameplay wrapped in graphical hype which ages pretty poorly as far as appeal qualities go.
So many adventure games tried to be Myst afterward that the sheer budgetary costs and redundancy of the also-rans crashed the adventure game genre for years.
The moral of Undertale is that children who are beaten shouldn't fight back
Anyway I completely failed to understand the sparing mechanic because Toriel was the one to explain it and I correctly pegged her as an abusive hypocrite. I thought she was talking complete nonsense when she told me to practice talking with a wooden dummy. If she wanted me to believe in nonviolence maybe she could have not used violence to rescue me from Flowey.
I killed Toriel and nobody else when I played it and stand by my decision.