This one gets a positive response from me. A good example of how to achieve a "slow boil" story, yet retain the reader's interest.
I loved the unsettling dimensions of the bookstore - but I am a sucker for effective, horrific architecture. I loved the underground passage and the bizarre underground sea (guess what? I loved "The Festival" by HPL too).
Only gripe might be that certain words were very close to one another (within a sentence or so) "wall" and "wall" or "face" and "face." Also, the story slowed down a little in the middle when some of the exposition reared its ugly head.
I actually felt things were a little too explained, the exact nature of the book could be left a little more mysterious. But then, I hate vagueness too so I was pleased with the direct nature of the explaination. Sorry to be schizophrenic about this point.
The story as a whole reminded me hugely of "The Horror at Red Hook," and "The Festival" by HPL and (a little) of House of Leaves by Mark Z. Danielewski and, of course, "Indiana Jones and the Last Crusade" (the immortal guardian part, anyway). I suppose I would have liked a slightly more grotesque ending, but that's really just a personal thing (and would have invited waaaaay too many comparisons to "The Festival" anyway).
Ultimately, I really liked this one. It might make the top 10.
Oh, EXCELLENT narration by the way.
EDIT: Mein Gott in Himmel! I just realized who the author of this one was. I swear it was not a coincidence. Anyway, I just want to say that, of the two stories, this one is definately my favorite.