Published by Wizards of the Coast.
This is generally thought to be the granddaddy of them all, 1978’s Tomb of Horrors. This is what separates the full from the demi-, the wheat from the chaff, the quick from the dead. Mention the name of this module to a gamer of the old-school variety, and the response is likely to include a list of the fallen and a blank stare of, well, horror.
The background is simple, in its way. As the background section says, “Somewhere under a lost and lonely hill of grim and foreboding aspect lies a labyrinthine crypt. It is filled with terrible traps and not a few strange and ferocious monsters to slay the unwary. It is filled with rich treasures both precious and magical, but in addition to the aforementioned guardians, there is said to be a demi-lich who still wards his final haunt.” There it is.
Read the Full Review at Dragonsfoot
While it might be an exaggeration to say that 1978’s Tomb of Horrors is the greatest D&D module of all time — though the case could certainly be made — I think it is fair to say that no other module is a better Rorschach Test of one’s gaming sensibilities. By the time I first encountered module S1 in 1980, it was already legendary as the ultimate “killer dungeon.” That alone ensured that I would buy and inflict it on my players, both because I wanted in on the excitement and also because I knew my players would love a good challenge. As it turns out, they liked it well enough that they threw multiple waves of their characters against it until, after weeks of attempts, they succeeded in making it to the end.
Read the Full Retrospective/Review at Grognardia.