I also felt an urge to see The Legend of Hell House again and thanks to Comcast's rewards program I could rent it for a dollar, although sometimes TCM shows it around this time of year. I think it is a genuine horror classic and seeing it again confirms this opinion for me.
The resemblance to the Jackson novel are close although Matheson's story is pulpier in both versions. Hell House is also a lot harder on its occupants than Hill House. (I'm going to pretend that the 1999 remake of The Haunting does not exist.) Matheson does leave out the scrungiest items from his book, like the Bastard Bog in which Belasco's lady orgiasts drown their unwanted offspring. I think there are some sequences that are genuinely scary, like the black cat going after Florence, but it's not a BOO! kind of movie. The ending is a terrible letdown.
The movie looks very good - love the red bedrooms. I agree that the acting is good except for Roddy McDowall. Not my idea for the part and I also think he's over the top here. I always liked Pamela Franklin in The Prime of Miss Jean Brodie and I like her here, too.
Speaking of Shirley Jackson, this Halloween season I saw the relatively recent movie version of We Have Always Lived in the Castle. Watchable but it doesn't work. The translation to the screen and the loss of Merricat's highly unreliable narration tends to highlight the many improbabilities in Jackson's plot (how on earth did Constance get acquitted?) and the acting is uneven. I think if they had taken a few more liberties with the story it might have helped, but the atmosphere is just not right.