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.
In Halo ODST it turns out that Huragok are slaves actually and there might be something to be gained by saving them from the covenant instead of killing them like you have been the whole game. The lesson here is that you should stop and think instead of uncritically participating in the cycle of fascist violence.
In Halo Reach, Noble Team try to go down in a blaze of glory defending Reach, but Halsey gives them an AI she says has the secret to winning the war, and it turns out Cortana has the coordinates of Halo. The lesson here is that you should stop and think instead of uncritically participating in the cycle of fascist violence.
In Halo 4, Captain Del Rio doesn't want to risk damaging the Infinity because it's a ginormous phallic substitute for his fragile masculinity. Chief and Cortana have actually been spending their time exploring and studying the lore, and they go rogue and save the world. The lesson here is that you should stop and think instead of uncrtically participating in the cycle of phallic symbols
What can I say, the bungie era had better writing