Great Game, but an even Greater Story
SPOILER-FREE REVIEW
This is a text-based adventure game, similar to games like Phoenix Wright or Hotel Dusk. So you will be reading 75% of the time. A game like this would not work if the story and the writing weren't excellent. Thankfully, 999 has some of the best writing and the most mind-blowing story in any video game you will ever play. It seamlessly combines elements mystery, thriller, and science-fiction into one truly compelling experience from start to finish to start to finish to start to finish...
I say "start to finish to start to finish" because to get the most out of this title you need to replay the game several times. And this game truly redefines "replay value", turning replay into more than just something you do for just giggles.
Outside of the narrative element are the locked room puzzles in the game. The puzzles are a good balance of critical problem solving while not being too obscure and difficult. This part is essentially a point-and-click (or tap in the DS's case) adventure where you find items in the room that ultimately help solve a puzzle that unlocks the room, allowing for your escape. It is often during these parts that the narrative diverges into more scientific and philosophical territory that at first sounds like irrelevant to the main plot. But if you take the time to achieve the game's "true ending", you will see everything converge into an exciting and thrilling climax where all the of philosophy and science become the most critical aspect of the narrative.
It's difficult to describe the game without giving any details about the story, which is so well-done and well written that it would be a shame to spoil any of it before you play it. It is best to go in with no knowledge of the plot to get the most out of it.
Play this game. If you like getting your mind-blown every once in a while this will do just that.