Ultima Underworld: The Stygian Abyss in 1992 was I think the first PC game I really obsessed about. From the first-person 3D (well, 3D environment, 2D sprites) combat, the runes and repairing items, it was an early "immersive" game. I took copious notes as well as buying any games magazine that had gameplay tips. Its sequel, Ultima Underworld 2 (1993), never really captured me in the same way.

Apparently a sequel to both was released in 2018 but was considered, charitably, "unfinished": https://en.wikipedia.org/wiki/Underworld_Ascendant -- What an ignominious ending to a well-loved series.