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.
I have no idea if this will affect your opinion of the series positively or negatively but here's some information that recontextualises the religious themes:
Humanity are actually the descendants of the gods of the Covenant religion, and explicitly hold an honoured place within the philosophy practiced by those gods. The covenant are trying to exterminate humanity because the religious leaders are suppressing this information from the general population and using genocide to keep their secrets.