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.
I remember when Tribes had the full title Starsiege Tribes and was vaguely related to the now forgotten "MetalTech" franchise that started with EarthSiege and BattleDrome.
Also remember Cyberstorm? Amazing Hex based mech game.
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.