Read for free on the Internet Archive here!
(And at the Open Library here.)
Although I overall would say that I like Shirley Jackson's We Have Always Lived in the Castle more than Hill House, The Haunting of Hill House has become a classic gothic horror novel, and if only to be able to see for yourself what it's like, and how it has influenced other books, films and series in the genre, I think that it is definitely worth reading. I found the descriptions and characterisation of Hill House itself to be the most interesting part, how it influenced the characters, and how it was treated as almost more an entity than a building, the ultimate focal point and drive for the story.
(I will update this with quotes and other thoughts after I have re-read the book. :] )