It's pure art and very difficult to explain what's so great and engaging about it.
At its core the game is a hiking simulator with some lovecraftian horror injected here and there, long well directed cutscenes, a mysterious sci-fi setting with some Japanese silliness on the side (dialogues and names are anime level stuff for instance), outstanding (almost next gen) graphics and orgasmic audio, both in environmental sounds and soundtrack. Acting is top notch as well.
If you're a person who likes walking in the country side, loves slightly slower than normal paced games and you're a little introspective and/or introvert there's a huge possibility you'll love this game to death just as I do. If you expect another metal gear or some kind of post apocalyptic witcher 3 don't buy it now and wait for a sale later on, because it still needs to be experienced. It's an unique experience.