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.
That one was bleak.
Prometheus was the bad guy supposedly but you're corpo officers leading subjugated "bioderm" genetically engineered clone soldiers around. One of the "hero" ones with better stats is based off of an unsuccessful John Brown type who got his genes "biodermed" as well.
All of them were pretty bleak with no real good people and no way out of a mutually genocidal war of violence that...well...humans started.
I don't disagree but CyberStorm really drove it in just how fucked everything was.