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.
As someone who loves RTS: Anything Age of Empires. Everything looks the same, yet there are dozens of civs to pick and they all just differ in boring-ass buffs and a few unit choices. The visual short-hand is terrible and reading what's going on in a fight or base at a glance is impossible for me.
AoE2 has an active player base and the casting overlays have been upgraded in the last few years so I sometimes watch games. Never really was able to get into the game.