Metal Gear Solid 2: Its plots had elements that now seems like predictions of the future, which is now coming true and has been for a while. I think I recently read that Kojima never intended it that way, but regardless, that's some good scenario writing there for it to be actually coming true in some ways.
Demon's Souls: It created an entire genre at a time when most genres were already well established.. What more is there to say? I could also list some other games that created genres, but it's easier to create something new when the industry isn't very mature yet, so for the purposes of this thread, that might be a bit boring.
Half-Life is often hailed for its role in bringing actually interesting plots to shooters, and I guess environmental storytelling as well? I don't think I have enough experience with the shooters of those days to fully verify this, but its reputation for this is probably well warranted.
I really want to say Battlefied: Bad Company for the destructive environments, but I don't think destructive environments ever really caught on big time. Also, it's unclear if I should give the credit to the first Red Faction instead, but destruction in it felt pretty limited compared to Bad Company, if I've understood correctly (I haven't actually played the first Bad Company besides the demo). I guess both are kind of pioneers of a feature that never caught on properly.
There's probably some great examples from the 80s/90s that I'm not aware of or simply don't remember right now.







