Right now i'm going through Temple of Elemental Evil, and getting close to finishing it for the first time.
There's something really special about the atmosphere of this game. Hommlet feels as sleepy as you can get. Nulb feels like you can be knifed around any corner. Every area is densely packed with lore and hidden quests or NPCs, and there are a million ways to go about tackling ToEE's relatively linear story. Some background information or character lore you won't ever encounter until you start a new game with a different party alignment. There are companions around every corner, and you never stop meeting new ones, even until the end of the game. Some of them will betray you, others reward you. It's an incredibly addicting experience if you go into it from a role-playing mindset. The fact that it is set in Greyhawk, the unloved older brother of the Forgotten Realms that was invented by Gygax himself, only enhances things.
In fact, I could go on about how Hommlet might be one of the most believable villages in any fantasy game. Almost nobody in the village, already large by video game standards, has some generic name, unless they are a kid. They all have some sort of employment, like a wainwright or a beer maker. You see their farms and they are willing to talk to you about their businesses. Nobody asks you to slay 5 goblins and bring some proof back. They have more realistic concerns, like the girl they want to marry belonging to a different church. Or not having a proper barn for their work. You have to put in a little effort to seek out the excitement, and that's not a bad thing at all.