Zork Nemesis is extremely underrated for its writing. It's an unusually somber and dark tale for the otherwise cheerily deranged Zork series. The quality of the acting in the cutscenes is also way above what was common for FMV at the time. Make sure to use ScummVM to play the game, the Steam release is barely working on modern computers.
View: https://store.steampowered.com/app/571060/Zork_Nemesis_The_Forbidden_Lands/
Since people are mentioning RPGs in a thread about PnC Adventure games I thought I would mention one of my favorite games in terms of writing: Realms of the Haunting. It's a fairly unique mix of PnC Adventure and... a FPS. IMHO it leans more towards adventure, though, since the combat is fairly trivial and kinda boring.
There is an absolute shitton of writing in this game. Not only are there numerous and long cutscenes with lots of dialogue, you can also look at most items in the game world and get some snarky description or even more little dialogues.
But most of the great writing in this game is unfortunately optional, as there are numerous long and detailed conversations you can have with your companion as they speculate about each and every new piece of information you gather, and they are fully voiced. More and more of these dialogues are unlocked in the menu as you go through the story and it's IMHO one of the best features of this game.
View: https://store.steampowered.com/app/292390/Realms_of_the_Haunting/