I actually haven't read this book in ages, but I've read Otranto and Udolpho quite recently (indeed, we were discussing Otranto in the Gothic Literature group). However, what makes/made The Monk Gothic to me is its sheer excess--how flagrantly Lewis thumbs his nose at Enlightenment sensibility and drowns the narrative in devils, horror, rape, and other scandalous plots. Much of the book is a bit tongue-in-cheek, just like Otranto; it's not meant to be 'great' literature or earth-shattering tragedy. Rather, it's supposed to give a thrill and reminds us of Goya's maxim, "the sleep of reason produces monsters." This is what happens when you expect people to live good, productive little lives and read books with tidy little morals...all your daughters will run to the bookstores and gobble up 'The Monk,' since it shows them pure, unbridled emotion for once. It probably worked a lot like manga does today, which features a lot of silly, over-the-top violence and even pornography; it's a release valve for the darker impulses of our society, which once read about, help us deal with them. Nothing is more Gothic to me that than--a way to acknowledge the beasts that live inside us and letting them run around a bit on our heads, even if The Monk is fairly tame to us now. I agree with you, though, it's a much more Gothic work than Udolpho, which has to explain all the terrors away; it all 'makes sense' for Radcliffe, whereas for Monk (who had lived in the Caribbean and overseen slave plantations) the horrors of the world were all too real, and he didn't want to shy away from that.

I agree--it's a work that, though dated, we can appreciate much more now than readers could 100 years ago. It's very 'modern' in a certain sense because of what you describe. Lewis's story is a lot like Beckford's Vahtek, both works of violence, sensuality, yet a kind of Romantic reality. Later Gothic works would temper this attitude behind a more Classical resolve, as in Frankenstein, even though that work is also in debt to The Monk for much of its narrative (and Shelley and Monk knew each other well).

I've never seen or even heard of it! How interesting...

I'm pushing my way through Clara Reeve's The Old English Baron, a slight re-writing of Otranto right now. It's 'gothic' chiefly by its use of a quasi-Medieval setting and some rumored ghosts and spirits. Not a great book by any means, but it was one of the first books, after Otranto, to call itself a "Gothic novel."

I'm also just starting Stoker's novel, The Jewel of the Seven Stars, about a mummy that awakens in Edwardian England looking for revenge. Have you read it? If not I'll let you know how it goes...sadly I've only read Dracula by Stoker (and that many, many times).