For a rulesbook that costs nothing, "The Void" is a bargain. It is clear to me that the authors want to make money with the sourcesbook after giving away the core book for free; so I did not expect the core book to ceover each and every question in detail.
Nevertheless, "The Void" suffers from multiple flaws. The crucial question how much a Warden (player character) knows about the occult nature of the universe is never answered. It is the Warden's Job to fight monsters but it is never stated how much they know about creatures, cults etc. or which of the Monsters given in the rulesbook are already known and what is known about them.
The skills "Occult" or "Cryptozoology" may be useful but there are no clues how to actually use them.
The example characters have flamethrower and combat shotgun; both arms do not appear in the "weapons" section, however. Especially a flamethrower should have special abilities like hitting more thsn one target, follow-up damage by burning etc.
The rating for the Warden armor is 10/5 on sample characters and 10 in the "weapons" section.
The rules for madness are very superficial.
Over all, "The Void" is too superficial in many ways; unfortunately, even in the "Secrets of the Void", this continues. If you want to play "Monster of the week", fine. If you want more depth, "The Void" only scratches the surface.
"The Void" as a setting is promising but lacks substance. It's like peeling an onion shell by shell with the authors giving you only the outer shell.
I am also disappointed that the authors seem to reduce horror to monsters that eat you or kill you, i.e. blood and gore.
The the mood of a Lovecraftian background, however, is absent.
[3 of 5 Stars!]