First of all i have to say that i don't like the lovecraftian things, either in their pure form or in the form that PF uses them.
For some reason when Lovecraft makes his appearance in PF the encounters are going to be weak (extremely so), that was the case with Shattered Star 5 Into the Nightmare the Rift and that's the case with Valley of the Brain Collectors, fortunately the encounters aren't as weak as they were in the Into the Nightmare Rift but they are still weak and you need to beef them up considerably in order to not have the game being a walk in the park.
This book is the conclusion of act 2 where the heroes learn more about their enemy and finally gather the means to go and confront the evil that's about to befall the world.
The overall story is there, although it's lessened by the sandbox-ish nature of the book.
The technological aspects and themes are well presented albeit at a much lower ratio than in previous books.
To sum up, i didn't very much liked this module and i would have rated at 3 stars (or less) but the article on alien technology and the article on Dominion of the Black were both superb, so the final rating of the book bumped up to 4 stars.
Wrote a lenghty review but the system ate it.
Long story short it's a good module, good asthetics, good dungeon ecology, interesting story but keep watch because it comes very close to having it's battles being a boring cakewalk.
I have to be honest and say that while i was reading this i was very dissapointed, from pretty much every aspect, but i was happily surprised when i actually run it and everything turned out well.
In contrast to the Fires of Creation (book 1) this module takes the heroes into a Mad Max type settlement in order to present them with threat of the adventure (the Iron Gods) and thusly concluding Act 1.
It also has a (very small) section that really evokes Dead Space vibes but unfortunately it's optional and very very small.
It has some sandbox elements that i didn't like, but it might be me since i don't like neither to play nor run sandbox campaigns.
Almost all of the encounters play very good (difficulty-wise) with a couple quite difficult encounters, keep in mind that (imo) this is true because the PCs are with same gear as they were in the previous book.
If you are one of those GMs that want and can build upon what you are presented then you would be very happey with Lords of Rust because it gives you a little information about a lot of things in Scrapwall but it's not fleshed out, so if you want you can do it yourself.
I don't give this module 5 stars because it wasn't much fun for me reading it (i was more engaged when i read the article on Technic League than i was in most of the actual adventure) but fortunately both me and my players had fun when i run it.
It's something very different than i expected (i expected to continue the themes present in Fires of Creation) and it turned out differently in play than i expected after reading it.
Summary: A very good part 2, now let us see where how this adventure path will continue.
I should have liked this book, but i didn't.
I am not sure why i didn't like this book, i liked the previous one, i liked the protagonist, it has a party, high level characters, it has religious themes present (although a far cry from the previous ones), magic and spellcasting, it has a magical a magical dungeon, an uber artifact waiting at the end of the dungeon, i really should have liked it with all of that... but i didn't.
There were a few things that i noticed being annoyed by like the number of characters (too many in my opionion) but the thing that i felt annoyed me the most was that the story doesn't have a strong identity. It isn't the personal struggles of the protagonist, it isn't an action story, it isn't a rebel story, it isn't an action story, it isn't a mystery story, it tries to be all of the above in one book and that in my opinion dragged it down because not one thing was complete. It isn't about the personal struggles of Isiem because it spends very little time showing us his morality problems and his thoughts, it isn't an action story because it has very few action scenes (including battles) and those that are in; are far way from each other, it isn't a rebel story because the protagonists quickly leave the rebellous city, it isn't a mystery story because it doesn't give any real clues*.
Keep in mind that last few chapters are great, i truly enjoyed them but it was too little too late, the story has already left a poor taste in my mouth.
And it really hurts the mystery part of the story when you give away the answer in the cover, from the moment we were given the first inch of a clue (the "they found something older than demons in the abyss") i managed to add two and two together and guess that there were researching qlippoth.
Very good start, sets very good tones, it has a lot of sci-fi trappings and even some cliches, the presentation of a crashed space ship is very good and it does a very good job blending standard fantasy with sci-fi.