Top three from stuff I've actually run (with more or less spoiler-free notes here) that was fantastic:
B10 Night's Dark Terror - Originally for BECMI, I ran it about 20 years ago for a 3E party. It's a BECMI module, but as I recall, the extent of my "conversion" was simply grabbing the 3E versions of monsters from the Monster Manual and plugging those in instead. The scope of the adventure is incredible, and it has so many different vignettes that allow you both intimate moments and sweeping, epic moments. The group LOVED it. This one is probably my all-time favorite among adventures I've had the pleasure of DMing.
B7 Rahasia - Also originally for BECMI, ran it about 2-3 years ago for a 5E party. Again, "conversion" was mostly grabbing 5E versions of monsters from the MM and plugging those in (and stealing some ideas online for a 5E versions of the Black Opal Eye). Party had a hard time adjusting to the tricks of the temple, but really got into the adventure (and were upset when the miniboss, who was set up as the BBEG, got away).
N4 Treasure Hunt - Originally for 1E, ran it about 7 years ago for a 5E party. Had to work a little harder to convert this one, as it assumes characters start as 0-level characters, which aren't really supported in 5E, but turned out pretty well. The adventure was memorable, and I ran it for my son and his high school friends on a weekend because they wanted to see what D&D was like. Me running that adventure got their imaginations going and they started a D&D group at the high school (which they DM'd, not me).
DDA3 Eye of Traldar - In the process of running this in PF2E, players seem to be having a blast. Converted this more heavily than the others, including replacing maps as I am moving to a VTT-like structure to run this and wanted to use better-looking maps than B&W ones in the module, but ran the first half in "theater of the mind" and that worked great as well.
B6 Veiled Society - Originally printed for BECMI, ran in BECMI about 40 years ago. Still one of my favorite modules as it's not your typical hack-and-slash. Professor DM's "Reviled Society" looks like a great 5E conversion -
CM9 Legacy of Blood - Originally printed for BECMI, ran in BECMI about 35-40 years ago. One of the best modules I've ever seen for "managing a kingdom" for high-level play where the dangers aren't simple monsters but instead the ill will of the peasants you are nominally ruling over.
The Lost by N. Todd Antil - I mentioned it here (
Best 1st level adventure out there) over 20 years ago, and I don't think it's around any more (I still have my PDF copy), but I found it a great introductory adventure for 3E (and played it in 3E). Very flavorful and could be dropped in almost anywhere when you need to get a holy relic into the hands of the party.
As can be seen, I usually utilize the maps, plot, and structure of modules, the mechanics bits are mostly monsters and traps and monsters at least are easy, just steal stuff from the MM and you're fine. IMO great adventures are less about the mechanics and more about a compelling plot, memorable characters, and exotic settings IMO. Players glom on to those more than anything mechanical. They might remember a spectacular crit or an enemy failing a save at a critical moment, but it's more likely they'll remember some weird idea they had that you as the DM didn't have a simple rule for and had to improvise a check for (what happens if you're being chased across a rope bridge that passes between two waterfalls while being chased by gnolls and the party's cleric decides to use "control water" to "raise water up" and "change the horizontal direction by a factor of two" in order to redirect the waterfalls on to the bridge where the gnolls are?), so I've found mechanics are not so important.
Modules I've read that I think have all the right plot elements to be amazing but which I've never had the pleasure to run:
- Red Hand of Doom (3E, finding a way to somehow combine this with Night's Dark Terror could be AMAZING)
- Ravenloft (1E, played it in the original 1E when it was still new, but never DM'd it so don't know how it runs, but the story elements are excellent)
- Keep on the Shadowfell (4e)
- L1 The Secret of Bone Hill (1e)
- DA1 Blackmoor (BECMI, I think the central location here can be a great source of both creepy horror and magical wonder if DM'd in the right way)
- Ruins of Gauntlight (PF2E, first adventure in the Abomination Vaults adventure path) - I haven't read the rest of the path yet, but this one looks excellent.
- X1 Isle of Dread (BECMI)
- Sunless Citadel (3E)