Oh, I remember Myst. That's one game unlike any other of its time, even if the software it was built on was very primitive.
You want hard? Play Riven. Play it for a week and watch your hair disappear, your sleep go out the window, food and water become secondary and all life being drained out of you by those accursed islands!
I could look at an puzzle/exploration game in the face, once.
Though it still looked beautiful.
i beat riven without ever looking at guides.
took me a year.
got all the endings.
i spoke fluent D'Ni by the end.
i understood the crazy moon language the islanders spoke.
i read the novels.
i hung out on the cyan forums.
i was a crazed myst-verse fan.