Nothing happens for a very long time and it is magnificent. I want to be clear that this is a recommendation, because the sentence does not read like one.
The castle is the character. Everyone inside it is furniture with opinions — elaborately carved, immovably placed, creaking under the weight of rituals nobody living remembers the purpose of. The book's central joke, if a book this solemn can be said to have a joke, is that the ceremonies have outlived every reason for performing them and are performed anyway, immaculately, forever.
The prose is the plot
You do not read this for events. You read it for sentences that take a corridor and make it geological. There is a description of a kitchen in the first fifty pages that I have thought about, unprompted, for years. The prose has a density that rewards slowness and punishes absolutely any attempt to skim; hurrying is the only way to fail this book.
Some books are a road. This one is a building, and the pleasure is in the walking round it.— The Editor
Who should not
If you need a protagonist to want something by chapter three, this will infuriate you. The ambitious young man who eventually supplies the plot does not properly arrive for a long while, and when he does the book is almost sorry about it. That reluctance is the point, but the point does not make it faster.
I would also say plainly: it is funny, but the humour is dry to the point of dust, and it does not announce itself. Readers who miss the comedy tend to find the whole thing unbearable, and I understand why.