Even though they market the Alien as unpredictable, it is kind of predictable to a certain degree, even on Hard difficulty, Nightmare is a different experience on a whole other level. With the unpredictable AI mod, A:I can be truly nerve wrecking, especially if you play alone, in the night, in a dark room with no ambient sound using a surround sound headset. Gotta warn you though, if you come looking for jumpscares, this game will disappoint you, but it makes up tremendously for its lack of cliché jumpscares with its extremely well designed atmospheric horror elements. It's a worthwhile buy, although in a sale because the DLCs on steam cost a lot.