Excellent, eminently playable supplement. Loaded with atmosphere and imagination, this can be dropped easily into just about any game or campaign. The Library can function either as a brief side-quest or visit or be expanded into the site for a full adventure.
Would love to see a 5E conversion for the monsters, but that's a minor quibble. Tons to love here, and makes a great addition to any DMs toolkit.
[5 of 5 Stars!]