I have to say that this is not an impartial review as I am a great fan of the Cthulhu and Lovecraftian Mythos, however I still think that it may be relevant for many interested on this material.
This review will not enconpass the adventure/scenario as I still haven't got time to play it.
Overview: I loved the athmosphere created by the layout and visual design of the
material. The rules felt really straighforward to anyone already familiar with the
"5th edition of the world's most famous roleplaying game". I liked the options of
letting go yith classes and focusing on backgrounds for this particular theme, as
well as I understand the choice of "Ancestries" insted of the more known "Races".
I enjoyed that it is filled with examples, as I am one that enjoy them very much, prefering to have some that are not useful than lacking one on something that ends up not being clear. I appreaciated the quotes used after tome chacpters titles, however I would like to have one for each chapter in case it was possible, I think they add to the vibe and genre.
The handouts look amazing and I really see the enormous value added by the GM's Sheet for Sanity Checks. For me pre-gens are a must for any quick play system or that intends to be played on the first session, so thumbs up for that as well. I have a lot to praise on this product and not that much to criticize to be perfectly candid.
Introduction: Describes directly and very well what the product is about. Loved the hint on the game that we "know the one". Plays upfront that classes are not used and that feats are one of the characters main customizations. Also, merits for mentioning that the lethality for the game is expected to differ as well as hinting on the most important chapters for already initiated players.
Mythos: Loved the flavourful description, including the ignorance as armour and the lucky or cursed references. However, I have to that as much as I agree with the boxed test of "The Problem with HPL", I found some of the phrasing confusing.
Character Creation: I was mesmerized by the backgrounds explanation, perhaps the best description of what backgrounds are that I have ever seen. The whole chapter is really straightforward and depicts in a clear and easy to follow way how to create a character even for inexperienced players. Enjoyed particularly the "Define Relationships" topic. The new mechanics for progression and how it is simplified and handled by the material seems to me a huge hit.
Ancestries: As already mentioned, I understand the choice of ancestries instead of race and think that it fits better on this case than for the "other system". It was a pleasant surprise to have one of the Saving Throws proficiency being chosen via the ancestry. I just felt that it lacked options, although it is not mentioned, I expect that, as with background, further ancestries options will be available on later material. I also did not felt that deep distinction in all of them. On top of that, I did not understand that if all ancestries are supposed to have two extra skill proficiencies, why "Experienced" is a thing and then we have also "Skill versatility". Perhaps the future options will clarify this designers' choice.
Backgrounds: Here it is explicitly mentioned that further option will be available on future materials. It details very well what is provided by choosing a background and despite some particular pet peeves of mine, I believe that the options are rich and interesting. Although I feel that Dilettante has some kind of an upper-hand during my first read, but I believe on the designers and that my concerns are undeserved.
Feats: I have to say that I saw some of the designers' public notes for what they wanted with the feats and I have to say that I loved it. It fills the characters with particularities and give them things that they are particularly good at. Most of the options are pretty self-explanatory and they feel really easy to use. There is no wrong answer when choosing feats, only what you want from your character. The most complex feat seems to be Persuasive Zealot, which I really think if it is a charming effect, by would assume that not, by the wording. Also, most option are what are popularly referred as "half-feat" which certainly does not bother me.
Damage, Healing & Rest: Loved that it heightens the challenge by extending the time needed for each rest when compared to the basic rules as well as the value needed on Death Saving Throws (pay attention to it experienced players). It depicts very well how to perform each type of rest and which actions may break it. The lingering injuries is one part that I always loved to incorporate on my games and I think that it is well detailed and adds sweetly to the tone of the game on mystery and horror.
Madness & Sanity: The "crème de la crème" of the system. The material invests a great deal of pages on them and I have to say that I particularly approve it. The system seems fitting and well thought, also presenting details for each transient/short-term and medium-/long-term psychoses. However I considered the changes between madness and insanity a bit confusing and think that a bit of editing could clean it up for future versions of the text.It is important to notice that losing sanity can quickly turn into a downward spiral, but it only seems fitting for the premise of the material and game. Some small clarification for me can be also done on the rules for a character to "control themselves" on a high-stress situation and on some situation that incites a sanity check (like the Forbidden Knowledge and the Unspeakable Horror sections). The GM's sheet is a great resource and for me add great value to all the set of rules.
Conclusion: All in all, I very much appreciated the material and would buy it again given the chance. Both M. T. Black and Matt are amazing designers (I can't believe I did not know that Matt had worked on Tales of the Old Margreve as well as on material for Petersen's Cthulhu Mythos). I recommend it for anyone interested on investigative horror games with a familiar set of rules.