The Saltmarsh modules for AD&D were pretty well-known as, I think, highly reasonable adventures to run. They weren't the kind of huge adventures that threatened to blow up Greyhawk, but neither were they boring fetch quests for a standard dungeon crawl. They were unique, with subtle plot twists that added nuance to what appeared to be simplistic stories. They were updated for 5th edition in the Ghosts of Saltmarsh book, which I've run, both as a whole and in pieces, several times now. The first adventure, Sinister Secret of Saltmarsh by Dave Browne and Don Turnbull, invites player characters to investigate a mysterious mansion up on a cliff on the outskirts of the city. This is my review of Sinister Secret of Saltmarsh, with no spoilers, from a game master's perspective.
Rumour has it that the old mansion on the cliff is haunted. So the player characters boldly approach it to investigate. What ails the house is for the players to discover, and I won't spoil the details here, but the adventure is often, basically, an investigative dungeon crawl. Player characters move from room to room, poke around, and try to piece together clues about what's happening in the house. It's not quite the puzzle that Death House and House of Lament are, but then again it's miles ahead of poor old Lost Book of Mektar.
As with most house investigation adventures, what you think is happening in Sinister Secret of Saltmarsh isn't the whole story of what's happening. There's a lot to discover, and it's the discovery process that makes this such a fun adventure. I recently played the Mansions of Madness board game adventure What Lies Within, and it uses the same trick. The players are told at the start what the problem is, but through investigation they discover so much more.
I think that's where a scenario like Lost Book of Mektar goes wrong. Players are given a problem to solve, and the house serves only as a series of whistle stops along the journey to the obvious or inconsequential answers.
Sinister Secret of Saltmarsh lets players explore freely in a house, which to be fair is pretty sparse and yet contains several moments of intrigue, and then leads the player characters to completely unexpected narrative places.
Sinister Secret of Saltmarsh (like Death House) is a turning point. In just a single scenario, player characters can go from simple townsfolk to explorers with access to a whole world of adventure (or, on the other end of the spectrum, to casualties).
Interestingly, the Sinister Secret of Saltmarsh doesn't do anything particularly outrageous to become this catalyst of character progression. Sure, there's a little more to the adventure than what's initially prestented to the player characters but it doesn't go out of its way to complicate the story, the ways House of Lament or, to be fair, Death House do. It's a pretty straight shot, and depending on how it's played a lot of the adventure can be bypassed. I've run it so many times at this point that I think I've probably seen every possible variation (OK, probably not) but the adventure has never failed me yet. Players reliably have fun exploring the house, uncovering its secrets, over-thinking the mystery, and getting themselves into trouble.
As an opening adventure to further modules, Sinister Secret of Saltmarsh is perfect. It lets players discover how to play the game in case they're new to it, it lets player characters explore, and it provides lots of opportunities for the game master to adjust the game settings to keep the session fun.
As a house investigation module, Sinister Secret of Saltmarsh is, again, perfect. There's just enough of what you'd expect in a creepy abandoned house to satisfy, and just enough surprises to make you realise that things aren't always as they seem in the world of Saltmarsh, or indeed in a roleplaying game.