Written in 1794 in the space of ten weeks by a 19-year-old Englishman, The Monk is sensationalist, scandalous, racy, melodramatic, irreverent (was in fact called "blasphemous" at the time, of course, which made sales skyrocket) - and is considered to be one of the classic Gothic novels of the English language. It wins that honor in spades, in my opinion.
Quick plot summary: Ambrosio, handsome and austerely pure Abbot of a monastery in a Spanish city, finds that one of his novice-boys is actually a young woman in disguise. She gets past his scruples and seduces him, leading him down an increasingly criminal path to ruin, involving lies, rape, murder, and the aid of evil spirits. There's also some living-happily-ever-after for the innocent characters who were his victims, just to keep it from being a total downer. But it's way too delicious to be a downer anyway.
You know, I read Ann Radcliffe's The Mysteries of Udolpho, which supposedly started the whole Gothic-novel trend. (Or was it Horace Walpole's The Castle of Otranto that started it? Well, anyway...) Udolpho was hard to get through. It was exceedingly long, with seriously dense prose. And, in the end, all the ghosts and eerieness were explained away by smugglers hiding in the walls, or something like that.
Not so in Matthew Lewis. We've got ghosts, demons, witchcraft, curses, spells--and all of it is real. And to spice things up, we've also got intersecting love triangles, people getting locked in tombs, sex-mad monks, pregnant nuns, and the Spanish Inquisition. I ask you, what's not to love?
Granted, it's got the kind of high-flown dialogue you'd expect in an 18th-century Gothic novel: I'm sure no one, at any time in history, has ever actually said something like "Ah! Ambrosio, can I have been deceived? Can you be less generous than I thought you? I will not suspect it. You will not drive a Wretch to despair; I shall still be permitted to see you, to converse with you, to adore you!" (Oh yeah, it's got some weird Capitalization of Nouns here and there too.) But it's still a damn sight easier to follow than Milton or Shakespeare.
Goths who like their novels on the literary-classic side (but still with plenty of blood) should have a look at this one. Classic-lit buffs who like their novels on the bloody/Gothic side should also give it a whirl.
I owe a tip of the hat to Camille Paglia for bringing up this book in Sexual Personae, and illuminating the lurid daemonic charms of it, beneath the goofy melodrama. (Egads, did I just say "daemonic"? I've been reading Paglia too long...)
P.S. I read this book for free, as an e-text, downloaded from Project Gutenberg. Hurrah for copyright expiration!