On one hand, the ARG elements didn’t stop the community from figuring out the secret right away, and they leave players wandering around without a clue. On the other hand, that kind of mystery and insanity that it drills into your mind is one of the best things about it.
Silent Hills would have been great, sure, but I also couldn’t imagine it having the same impact P.T. did. It would have to be many hours long, with a story that can be easily parsed. IIRC there’s an interview with Kojima where he said that Silent Hills would have combat and wouldn’t be first-person. And as much as I like the series, there’s something regressive there.