G1, D1, D2, and D3 certainly deserve their fame. Not sure about G2 and G2 being such big classics as the others, but Q1 is widely regarded as junk, and doesn't actually connect to the plot thread that tied together the other six modules. It's also cheating, because this is a bundle of seven different adventures.
Ravenloft: A giant castle that looks really fun to explore, and I actually want to run it one day.
Tomb of Horrors: The Thing That Should Not Be. Tomb of Horror's is not an adventure. It's a convention one-shot meant for having a laugh at stupid death. Don't run this as part of a campaign.
The Temple of Elemental Evil: From all I heard, this one is infamously bad and basically unplayable.
Expedition to the Barrier Peaks: I actually don't know.
Desert of Desolation: I heard it's great.
The Keep on the Borderlands: Lots of people really love it, but I don't see why. The overall scenario doesn't make much sense to me. It's famous because it came bundled with the most popular Starter Box in the olden days. It's what a large number of older played first.
Return to the Temple of Elemental Evil: I don't know either.
White Plume Mountain: I think I read it and remember nothing.
Return to the Tomb of Horrors: I don't know this one.
Gates of Firestorm Peak: Neither this one.
The Forge of Fury: This does look really good and I had it ready to run for several campaigns, but the players never went there yet. Still keep it ready for upcoming campaigns.
Dwellers of the Forbidden City: I love the idea of this one. But it's really just the city streets of an ancient ruined city. You have to create all the interiors of the ruined palaces and the underground tunnels yourself. It's great for what it is, but it's more a coloring book for GMs than a ready adventure.
Dead Gods: Was this Planescape? I think this is the one Planescape fans fawn over.
Castle Amber: I read it once. It's famous. But I don't know why.
The Isle of Dread: Like Forbidden City, but a whole island instead of a ruined city. Fantastic starting point to build your sandbox campaign, but not an adventure in itself.
The Ruins of Undermountain: I believe a Forgotten Realms megadungeon. Somewhat famous I think, but I don't believe anyone's been praising it for being good.
Hidden Shrine of Tamoachan: A fun puzzle dungeon meant as a convention one shot, but this one actually works as part of a campaign.
Against the Cult of the Reptile God: This is the number one and there's no competition!
Scourge of the Slavelords: Heard of it, but never sounded appealing enough to read it.
Dark Tower: It could be that the dungeon itself is actually great. The book itself is a nightmare. It's a very early module, but no matter how long and hard I try, I just can't figure out what's going on there. Caverns of Thracia isn't easy to read either, but much less difficult than this one.
The Lost Caverns of Tsojcanth: Some fun ideas, but it comes across as a collection of somewhat random rooms to me. This is one that I want to do a full remake of from scratch.
The Forgotten Temple of Tharizdun: Probably my favorite dungeon ever.
City of the Spider Queen: I ran this one back in the day. The locations, creatures, and backstory are all actually quite great in my opinion, but at least as I ran it as a noob GM back then, it's mostly just a linear string of combat encounters. Cutting it all to pieces and turning it into something open ended with more complex NPC motivations could make something really great.
Dragons of Despair: Serious time: I actually think this was the greatest turning point for RPGs since their first introduction. But not for the better. This this is the cause for 38 years of railroading and people thinking this is what roleplaying games are supposed to be like.
The City of Skulls: Never heard of this one.
The Sinister Secret of Saltmarsh: All I know about this one is the twist, and I think it's lame.
The Lost City: I can appreciate why people like it, but another case of lots of random rooms with nonsensical puzzle situations glued together. The overall concept of what lies underneath it is pretty compelling, though.
The Assassin’s Knot: Don't know anything about it.
The Ghost Tower of Inverness: This one neither.