I just read "Silver of the Sea", was the first of the Wicked Mystery.
And I really like it. The number of NPC is easily handable and they are well described. The hints are good to find and the most important are hidden in more than one place to avoid bottlenecks.
I think it's not too hard for the players to understand the clues right. Tales like the "Fisherman and his wife" should be known to the players. Several countdowns are bringing the story to a decent pacing and this not too structured or railroaded. Okay, it won't deliver too many options or "red herrings" (pun intended) either.
The Lore mechanic enables them to get background information about the vaesen easily, especially if they managed to get the right advantages earlier in the preparation.
At the end, the characters have a moral dilemma and maybe are in real danger of losing the lives or mental health, but in a comprehensible way, other than most Cthulhu stories I know. Having a not to low Agility rating is vital...
The only thing I can't estimate at the moment is the vision of palace under the sea. Sounds a bit to magical, but might be good for the atmosphere.
What do you think about it?