So different from the book that it's almost a completely original work...

I agree. They shouldn't have titled it The Haunting of Hill House, and instead presented it as an original work, loosely based on the novel, and not bothered with using the same character names, which had nothing to do with the original characters.

Even putting all that aside, I don't get why it's being rated so highly, but, different strokes and all.

The book is brilliant -- a classic -- so is the 1960s film adaptation of it. They are both far superior to this.

If the showrunners had taken this in a different direction, and modernised it, the way Bates Motel did with Psycho (despite my initial misgivings), it would have won me over. But they didn't.

As Catbookss said, the original novel by Shirley Jackson is brilliant, *the* definitive haunted house novel. And Robert Wise's 1963 movie is very faithful to it; it's rightly regarded by many as one of the best horror movies of all time (it's one of Martin Scorsese's favorite films). The TV series isn't my cup of tea at all but each to their own. I highly recommend both reading the book and watching the 1963 movie though.

The 1963 movie is a very faithful adaptation, with very few differences. There will always have to be *some*, but overall director Robert Wise and writer Nelson Gidding perfectly captured the plot and tone of the book. The Netflix show, on the other hand, is basically a revisionist work. So much so that it begs the perfectly reasonable question: why bother? Why go to the trouble of securing the rights to the novel when you're going to throw out 99% of it and retain only names and a few lines?

This wikipedia article sums up the book...

https://en.wikipedia.org/wiki/The_Haunting_of_Hill_House

Except for some of the character names and a scene or two that pays tribute to the original book, there is no connection between the Netflix series and the original book/movie beyond sharing the same title.

I haven't read the book or watched the movie in decades, but the gist of both is that the house is a literal manifestation of the increasing mental instability and hysteria of the heroine Eleanour Vance. It's left to the reader or viewer to decide if her condition is the symptom, or the cause of the events in the house. It's similar to The Shining where Jack Torrance's descent into madness is matched by the increasingly supernatural encounters of The Overlook hotel. (Stephen King acknowledges Hill House as one of the inspirations for his book.)

There are no ghosts -- most of the stuff that happens is knocking, banging, writing on walls sort of thing -- poltergeist activity. The movie adaptation was pretty good and could more accurately be described as creepy a la The Babadook rather than outright horror.

No, although that would have made more sense than writing a completely different show and tacking on the name "Hill House" and some character names. A modern-day setting (with perhaps flashbacks to the the era when the Crains lived in the house) would have been interesting to watch.