My opinion differs somewhat. The first section at the castle was spooky and quite good. The rest of the novel was pretty boring. It was difficult to overlook the preachiness and casual racism and sexism. The epistolary format added an unwieldy layer of distance from the action and characters. Finally, the ending made no sense. They stabbed him with a knife and he turned to dust, but turning to dust was previously established as one of his powers. And stabbing with a knife wasn't an effective method to kill him.

However, I'll take this opportunity to give a shout out to Bela Lugosi and 1931's Dracula movie adaptation. It's worth a watch!