Honestly, it was everything. Creature design, the scareactors tending to be amazing, the set design, the facade and entrance way just setting the mood, and the general "Alien" vibe I got from it. It was pretty much the closest to an Alien house I feel we will ever get. Also I just love underwater themes so that helped. It was one of the few houses where I got so engrossed in the atmosphere and sets, and just general design of the house, that I forgot I was in a house and felt I was actually in an underwater facility.