Sirenswail is an OSR adventure intended primarily for use with Lamentations of the Flame Princess, although it is not officially part of the LotFP product line. It was written by Dave Mitchell, and you can buy it at Lulu. Full disclosure: I'm in the credits for this book because I read an early draft of the adventure and gave Dave some feedback, so I admit that I was predisposed to liking this one before I read the final version. That said, I really do think it's a great little book, and it's well worth picking up.
Sirenswail is a softcover book of 66 or so pages. It's got a classy, somewhat abstract cover by David Paul Hellings which (perhaps not coincidentally?) reminds me of the Mana Cross from Siren. Mr. Hellings also did the map and monster illustrations in the book, which may look a bit amateurish but are appealing to me all the same in their slightly cartoonish and yet somehow woodcut-like style. The map is pretty clear to read and includes a handy hex grid. The rest of the art consists of old public domain material as far as I can tell, but it fits the setting and tone of the book just fine. Sirenswail is "An adventure intended for 5-8 characters of levels 1-3." The book contains "Adult Material," in case you're wondering. A note in the back suggests that this can be used as the first part in a series of upcoming adventures by Dave Mitchell, but it definitely works on its own merits. I see no reason that Sirenswail couldn't work as a one-shot or as something to slot into a larger "non-Mitchell" campaign, and the book seems to be primarily intended for such purposes. I see no signs of any invasive meta-plot.
Sirenswail is what I would call an investigative adventure. The closest thing to a dungeon consists of three rooms, but the real meat of this thing lies in NPC interactions and poking at various mysteries. This is certainly not a bad thing, as evidenced by LotFP adventures like "A Stranger Storm" (from the free Referee Book), "In Heaven, Everything is Fine" (from Forgive Us), and England Upturn'd. Sirenswail offers a lot of interesting NPCs who may either help or hinder the adventurers (and each other) depending on the party's actions. The NPC write-ups are efficient, providing useful motives and traits without taking up a lot of time or space. Many of them could just as easily wind up as friends or foes to the party. Considering that Sirenswail is openly based on the 1973 movie The Wicker Man, the "peaceful" island community is not what it seems, of course. I don't want to spoil too much, but the characters are a big strength of this book.
The book begins with a brief history of the setting - England, 1644. There is more historical information a few pages later, which specifically details the town of Penzance on the coast. This information could have probably been condensed into one or two fewer pages, but it's not a big deal because the book is already a quick read. Most of this isn't strictly necessary, but it's helpful for flavor and for answering a few general questions that might pop up about the setting during play if neither the DM nor the players know much about this time and place, as is the case for me. Between England Upturn'd and Sirenswail, I feel like I should have enough information to start a good campaign in Early Modern England without needing to bury myself in textbooks first. Sirenswail could probably plug into England Upturn'd pretty nicely as a sort of side-quest, now that I think about it, although I'd have to double-check both books to be sure.
The adventure itself is split into three segments, and these can actually be used independently of each other. First, there's Penzance, which depending on the wishes of the DM could serve as either just a jumping-off point for the adventure, a hub from which the party could pursue multiple adventures, or a location for a short urban adventure in its own right. There's a tavern and a weapon shop with unique and detailed price lists, as well as some really good random encounters and rumors. The DM would have to do a little extra work to make the party's time in Penzance an adventure all by itself, but the book provides good inspiration and decent guidance.
The second segment is the voyage from Penzance to the titular island. The book basically says you can either gloss over this journey or make it a bit more eventful. There's a table of random encounters (or perhaps adventure hooks) provided in case the DM would prefer the latter. Again, these ideas might need some slight fleshing-out, but you could use the table, the ship, or the NPCs in other nautical adventures if you don't want to run the rest of the book.
The last segment takes place on Sirenswail, or as the residents call it, The Island. This is the main part of the adventure and includes the bulk of the detail. Again, there is a new and detailed price list for The Island's inn, which is nice. Interestingly, The Island's head honcho insists on giving the party a brief tour when they arrive, which is a good way to present both the geography of the place and several plot hooks to the players. There's a pretty strange set of random encounters that could happen if the adventurers explore at night, which are quite creative and should keep the players on their toes. The adventurers will probably spend most of their time on The Island interacting with the odd residents or examining The Island's landmarks, however. This is definitely a slow burn kind of deal, unless the players decide to try and indiscriminately slaughter everybody, which I'm guessing wouldn't go well for first-level characters. If you want something other than the usual smash-and-grab D&D adventure, this should hit the spot. If you want a slugfest, you should probably look elsewhere, although Sirenswail does have the potential for a few fun and memorable combat encounters. Overall, Sirenswail uses a subtle kind of horror, with good buildup and creepy secrets to stumble upon.
There are a few more odds and ends I should mention. Dave Mitchell's writing style is clear and straightforward, which is good for something that needs to be referenced at the game table, but there's definitely some personality that comes through as well, which is nice. The hit dice for all of the NPCs/monsters are listed as the type of dice used as well as the number of dice (3d8, for example). Maybe this could be helpful if you're using the LotFP Playtest Document, in which hit dice are not directly related to character class. Still, the hit dice almost all seem to be consistent with the current LotFP Rules & Magic book as well. Not a huge detail, but I thought it was interesting and possibly useful. Also, I should mention that this adventure includes the possibility of a huge treasure haul for a group of low-level characters, but considering the difficulty they would most likely face in actually getting it off The Island, I'm not personally worried about it. Still the DM may want to either decrease the value of the main treasure cache or simply be strict about how much treasure the party can carry if this seems like it would be a problem. Honestly, I think it might be a really good idea to put most of the treasure in one gigantic pile and make most of the remaining treasure kind of piddling in this kind of adventure: It should keep the party invested in finding "one big score" before trying to escape, and I bet it would really bring out the problem-solving skills in your players once they find what they're looking for!
Finally, I do have a few criticisms I should mention in the interest of fairness. First, there's a section of the book between the historical overview and the Penzance section which serves to introduce the DM to the premise of the adventure. Unfortunately, it also includes some information that should have probably been moved to other sections of the book in order to reduce page-flipping back and forth at the table. At least this section could have included page numbers for the later sections this information references, and vice versa. Second, there's a slight inconsistency regarding a reward offered to the party for a certain action on page 9; is it 500sp or 1,000sp? Third, the adventure includes some boxed text in the form of sample dialogue for NPCs. I don't actually mind this, since the dialogue is presented as example material that the DM should feel free to change, but some readers might see this as a weakness of the writing, since boxed text seems to be frowned upon by many OSR fans. Fourth, one of the "monsters" can cause a small XP penalty to the person who kills it, which is something of which I'm not too fond. However, it would be easy for the DM to just make the monster worth zero XP instead. Finally, the adventure doesn't have any magic items for the party to find (unless you count a few traps), which is a little disappointing considering the tendency for magic items to be extremely weird, screwed up, and interesting in LotFP. Still, these are minor problems that don't come close to ruining the adventure.
I definitely think Sirenswail is a great addition to my collection, and a strong first adventure for Dave Mitchell. The price is certainly right: I think it cost me about $13 after shipping and handling. If you like the idea of The Wicker Man as an adventure for Lamentations of the Flame Princess, this should do nicely. I think it also works well as a source of ideas for other adventures in Seventeenth Century England, if that's more your thing.
Sirenswail gets a dead French monkey spy hung by nautical pagans out of 10.