This game is OK. The puzzles are not relatively to difficult. The only complaint I have is that the scenes in between each level takes forever to get through. It's a very creative game, but there is just way too much dialogue which makes the game seem longer than it really is.
This game has a fantastic story, with massive plot twist endings and logical theories woven into a tale of survival. Half of the game includes room-escape puzzles, with the other half being narrative text of the story. You don't need to have played 999 (The first game) to understand this one, but it really helps. There are some big story elements of the first game that are alluded to. Keep in mind that the story is incredibly confusing and gets more confusing as the game continues. For those that don't know about logical theories, such as Schrodinger's Cat, the game explains many theories with real-world examples to try and help you understand. Every character has a unique, engaging personality that never gets tiring.
Overall, if this is your kind of game and if you can keep track of all the chaos that happens as the game progresses, you'll find that the story is really engaging and leaves you wanting more.