This is credited to being the first Gothic novel. I enjoyed the book, I found it immensely entertaining. Princes and princesses, knights, a castle with secret corridors and trapdoors galore, not to mention a creepy portrait and a more than slightly unusual family, this is the kind of thing that fantasy is made of. I can see why it sparked such a huge and successful genre.
However, I can't help but feel that this is a caricature of a novel, a cardboard cut-out stage with two-dimensional characters. Walpole's characters are stereotypes that don't seem to show any emotion or even surprise. Realism is hardly the author's aim, though, so perhaps this can be forgiven.
This is a novel that is to be laughed at rather than with, I'm afraid, despite its profound effect on literature as a whole. If you're happy to do that, though, or to overlook the gaping plot flaws, it is a really enjoyable read. It is a must for any lover of fantasy or Gothic.