|My copy's monochrome pink cover|
prior to the revised green cover.
TLDR Summary: If you are not familiar with the history of Tomb of Horrors, or your players don't fully understand the stakes, just don't run it. PCs will die. If your players aren't expecting an abattoir dungeon, it will ruin your campaign.
So John Wick appears to have caused a bit of a kerfuffle on social media by posting that Tomb of Horrors is the "Worst Adventure of All Times".
A lot of people who love classic D&D (and anything Gygaxian) came out to defend ToH and in some cases attack John Wick.
I don't really have a dog in this fight... but I did want to say something about why Tomb of Horrors could be the worst thing you ever do to your players.
You see, Wick's article presents an entertaining read and the reactions of his childhood friends are pretty much what one would expect... but it's not entirely the fault of the module itself. It's the expectations of the players at the table.
In the early days of gaming, D&D tournaments awarded groups of players prizes at conventions for doing "the best" (in a competition sense) at an adventure module. The "best" often meant "who could get the furthest with the most amount of success [explored areas and treasure] and least amount of PC death." Tomb of Horrors is one such beast.
It's not intended or particularly suitable for an ongoing campaign. It's a one-shot adventure where the players should know they are going to be tested (née tortured) to the Nth degree. You don't just drop Tomb of Horrors on your players in the midst of a normal campaign because it is specifically written to be overly brutal to test a group's ingenuity.
This module is only suited for people expecting that particular style of play. There are many people who enjoy this play style. Dungeon Crawl Classics specifically caters to this style of play with its "character funnel" which basically means your PCs aren't worth the paper they are written on because of the 4 that you create, you'll be lucky if one gets out alive after the first adventure... and it's anyone's guess if he or she will survive the 2nd adventure.
It can be a particularly fun way to experience a D&D style game if that is what you are expecting from the outset. If the players are not expecting a maze full of instant-death traps, then it's just the DM being a d!ck.
So is it really the worst?
Depends upon whom you ask and under what circumstances it was played. The biggest problem with the module as a whole is that when it came out in print, it didn't explain itself well to the teen aged DM who might have thought that this was just another adventure you put your players through. It's not intended for a "casual" game of D&D. It has a particular goal to punish the unwary severely with a kick to the gonads. Multiple times. No save.
In that sense, it is the worst module you could ever inflict upon an unsuspecting group of players... Because no one thinks the DM is out to TPK the entire party every 10 feet of dungeon hallway, which is pretty much what Tomb of Horrors tries to do... and that kind of adventure does suck terribly if that's not the game you are expecting to play.
[Edit]: I have seen people on social media defending it as a "thinking man's dungeon", but honestly that's a bunch of baloney. There are a number of places you can just die, without warning, because of a failed "check for traps" roll. Not because you ignored clues. Not because you did something particularly stupid... but just because you were standing in a place where the dice dictate "it is time for you to die". No escape. No save. There's nothing that makes that a "thinking man's dungeon." It's just an example of poor game design.
Lastly, not everything Gygax wrote was gold. He was a human being who had immense vision, but was still an imperfect. Some of his writings are downright... Gygaxian... and contains so much purple prose that people had to invent the word "Gygaxian" just to describe it.
|Hommlet - 5e style|
As a one-shot, Tomb of Horrors could probably be a lot of fun with the right group.
Personally, it's not really my cup of tea despite owning one of the original monochrome cover printings. I'd rather go back an revisit the T1 - The Village of Hommlet (which I actually have been doing recently with my gaming group). That, to me, is the ideal Gygaxian adventure.