Over on Story Games, JBR made some very pointed observations about Tomb of Horrors. So I feel compelled to explain why I consider Tomb of Horrors to be one of the greatest D&D modules every written. Everything I need to make this defense is contained in the first hallway of the dungeon.
WARNING: SPOILERS ENSUE!
First of all, any given party is either going to examine everything carefully or they’re not. If they’re not, then this isn’t the right adventure for them. They’re going to die horribly and not have any fun doing it. The assumption of Tomb of Horrors is unmitigated complex deadliness. This is part of what makes it awesome, but only if that's what the players are up for.
If they are going to examine everything carefully, they’ll quickly find the hidden path and the poem that are the key to the entire dungeon and absolutely necessary to surviving it.
The path leads the party, first safely, then not so safely down the hall. The message is obvious. Careful observation will get your part way there, but not all the way. This dungeon actively seeks to mislead you. In the dungeon as in the hall, a careful party will get some distance on care alone, but only so far. Near the middle point, things will start to go horribly wrong. The poem, like the path, provides a step-by-step guide to several of the nastier perils of the dungeon and must not be ignored.
At the end of the hall, the party is given a choice between two unattractive options. The first is the demon face. While it’s conceivable that completing the tomb might involve a leap of faith into a dark abyss, it’s not an attractive option. It should not be chosen unless no other option is available.
The second choice is also unattractive, but perhaps not quite so unattractive. A party may be tempted to try it out (and most often at least one character gets separated here). Ultimately, however, the correct conclusion is that they ought to seek a better solution before they continue. Some heavy divination could be employed here, but it would be a dangerous waste of resources.
The instant that this conclusion is reached, the fiction of the game gives the players the correct answer. There is a big freaking door painted on the wall. If the players engage the fiction at this point, they will find the correct solution. If they don’t engage the fiction, but instead engage the mechanics, by looking for secret doors and so on, they will also eventually find the correct path.
This one room gives the players all the information they need to complete (or at least come close to completing) the Tomb of Horrors. It gives them the poem. It warns them that it will try to purposely mislead them. And it tells them that there are choices within choices. It engages them on the level of fiction and on the level of mechanics.
Tomb of Horrors isn’t for everyone. I fondly remember the all-nighter in which we defeated the tomb to be one of the best RPG experiences I’ve ever had, though I’ve also seen if flop. It is my brother’s all-time least favorite module. Your mileage may vary.