I should have read this ages ago, but for some reason I always suspected it would be dry and dull. How wrong I was! It's a blast. Totally bizarre, and lots of fun. It's been described as a combination of Arabian Nights and Voltaire, which makes sense, but doesn't give enough credit to the fascinating interplay of literary forms in the novel - particularly its engagement with romance as a genre. What struck me were the echoes of medieval quest narratives, transported into an "eastern" setting, and actually curiously inverted into a quest for sin rather than redemption.
One curious aspect of the book is Vathek's mother, who is in some ways the unacknowledged star, way more evil and sadistic than her son, and also way more invested in this whole pathway to doom. But for some reason, it seems, she needs Vathek to get her in the door. I don't know why this aspect of the book particularly struck me, but there is something really interesting about the way she functions as a character.
The overall tenor of the novel, despite its occasional attempts at moralizing, is unabashed glee and a kind of delight in the sheer evil of it all. In the Introduction to the edition I read, Mario Praz mentions Marquis de Sade, and it's an apt reference. Although Beckford doesn't go into that kind of detail, the cheerful accounts of horror definitely have a merry sadism about them.
It's also interesting to read a European account of a Muslim straying from faith. The novel doesn't exactly inhabit the eastern world, it's clearly more of a tourist, which allows, I think, for some level of indifference about the fates of the characters, but it doesn't explicitly describe them as barbaric or deluded either, the way other such works do.
It's a short book - just over 100 pages - and it's great fun, if you're into weird 18th century type stuff. Maybe even if you're not.