It's a good premise, the execution isn't much a "horror" but more like a mystery that happens to be inside a creepy mansion. There's several instances of body horror though so be wary of that. The main character is compelling enough and the mystery is beautifully done although it feels slow paced at the beginning and then too fast in the end.
I personally thought the ending was a bit corny, but I'm also not a big fan of horror anyway so.