It was better than I expected. A lot better, in fact! The gameplay was eh, at least pretty good, lots of puzzles involve fussing with Harry's phone in some way, but some of it is pretty clever. The plot is magnificent, however, and is the real reason to play it.
I understand why it's titled as a spin-off: it doesn't really intersect with the big themes and story of the other titles. It also strays from the gameplay tropes found in the rest of the series. Death, for instance, isn't in the list of consequences. There aren't any weapons, or health items, because you don't fight monsters. You don't fight them because you cannot win. You run. They chase. You look for the way out while hiding. I'll admit, I thought those sections were really exciting. Outside of the nightmare sections, you're fine.
I kind of wish life was like that. All the terror concentrated in short sections that you just charge through. And then you're okay, until it happens again. It would be better if there was no terror at all, but if there has to be any, I'd want it wrapped in such a way that I could cope with it. It's better than the ubiquitous creeping kind that I think a lot of us are constantly dealing with.