Is Tomb of Horrors an example of standard old school gaming, or is it a single outlier, an exception from the standard? Is Tomb of Horrors what gaming used to be like? Or is it something unusual, even unique from old gaming?
I believe it is one of a kind.
Much like Tolkien's imitators completely fail to capture the most important aspects of his text, the many Tomb of Horrors imitators fail to capture the most important aspects of the module.
There are LOTS of old school killer dungeons. IMO, Tomb of Horrors isn't even the most deadly of the old school dungeons. 'Ravenloft', 'Lost Caverns of Tsojcanth' and 'Hidden Shrine of Tamoachan' are IMO all harder to succeed in with characters in the suggested levels of play. And that's to say nothing of things like 'Grimtooth's Traps' and other silliness that resulted from designers inspired by TOH but who failed to understand what made it work. But Tomb of Horrors stands apart from other killer dungeons generally and its imitators specifically.
First, TOH is primarily a test of player ability and not of character ability. There is almost no combat in TOH. There are very few saving throws in TOH. There are numerous traps that by pass hit points completely. Until the very final encounter, which seems by intention to be one that the wiser player avoids, what is on your character sheet is almost irrelevant in determining whether you succeed in the module.
Secondly, this amounts to a spoiler of some sort, but Tomb of Horrors is fair. Acererak plays fair. He's so uncannily and unusually fair given his apparant goal (killing adventurers) that it had to be lamp shaded and explained in the game universe in 'Return to the Tomb of Horrors'. He's not using reverse psychology on the players to force them into guessing what's behind door #2. If you must guess whether to go left or right, then success depends largely on luck. Acererak follows a pattern and sticks to it, so that with care you really don't have to guess after you successfully enter the tomb. If success depends on hitting the target AC or making a saving throw or doing enough damage when rolling damage, then success is at least in part luck and even a party which makes the correct choices might still be defeated in the module. Tomb of Horrors is almost entirely singular in being a killer dungeon where this is not true. If you make the right choices, you can 'beat the dungeon' with practically a party of 1st levels. Of course, with 1st level characters you'd practically have to be perfect in your play, to the extent that I think no one could do it without having first read the text, but really to 'beat the dungeon' requires you to make no big mistakes in play anyway and so even 10th level characters only gain the ability to survive minor mistakes.
This is the main reason why Tomb of Horrors has acquired such a reputation. It really is entirely different from everything else. S2 'White Plume Mountain' is a killer dungeon, but its often a killer dungeon in the obvious sense of having very dangerous monsters. The puzzles are still there, but environment is reduced to being only an equal threat and challenge. A first level party even making all the right decisions still has no chance of defeating the module, because so many dangerous monsters stand in the way. By something like S4: 'Caverns of Tsojcanth' its almost entirely the dangerous monsters and the ability to make saving throws and use your characters abilities effectively that determines success. It's not remotely the same sort of dungeon.
