Lovecraftian horror. We have a bona fide Artifact Of Doom, and the game is an inexorable progression to an unspeakable end.
There are some nice touches to start off with. We start off, of course, not knowing who or what we are. Then we're told we have makeup on, and we (well, I) assume we're a woman. Then we're told it's part of a disguise. What? Oh, are we a spy? Wait, rotting flesh?? Boom, boom, boom. It's an effective way of grabbing attention and engaging the reader, by slowly providing these trickles of information and then subverting our interpretations.
There's at least one clever puzzle in this, I think: the one involving access to the tunnel. I actually stumbled onto this by accident, but the logic was clear.
All that being said, there are still a few holes. The holes in the code are minor: assumptions made that don't fit the situation. Story-wise ... I have to wonder, what is the significance of the key our grandfather sent us to fetch? Why a key, and what does it represent? Why were we allowed to take the book at all, if our grandfather thought it so dangerous? Should there not have been some compelling reason and game sequence in which we obtained the book from him? In that regard, it feels as though we've tumbled headlong into the Lovecraftian spiral into insanity without the usual journey to the brink.
Breakfast: a smoothie made from under-ripe bananas and papaya, I think, with some citrus and a pinch of salt for that certain je ne sais quoi. No added sugar. No toast to start. A few lumps, but the flavour seems about right.