First off I'd like to say that this game is AMAZING. It is like a reincarnation of an old school point and click game mixed with a visual novel. This is very rare to see nowadays since most adventure games have evolved into action games, RPGs, shooters, survival horrors, etc. But damn this game is so awesome!
The story is fast paced and interesting. You always want to see what's gonna happen next to the characters. Everything is at stake for them including their lives and to make matters worse they are limited by time (9 hours as the title implies) and no matter what you do someone is going to die (But who?).
The game offers 5 different endings. All which are worth seeing. The goal is to get the best one which the only way to do so is to see one of the bad endings and then you will get the good one.
While it's not heavy on gameplay the stuff you do is pretty fun. You have to solve puzzles usually relating to escaping a room or finding a clue that will lead your characters to draw a solution. It's mostly just pointing n' tapping with the stylus with a few mini-games.
However, don't expect this to be a puzzle game. The puzzles are just there to give yourself more details about the story. If you are looking for a game with complex puzzles then you've come to the wrong place.
The music is excellent and the sounds are great. Unfortunately there are no voices. It's all text. Just a fair warning. There will also be some translation errors, but it shouldn't bother you unless you are a grammar nazi.
The graphics are mostly still images, which again might bother some. However, they still manage to look great and the backgrounds are very realistic (at least for a DS game) The controls also work great to aside from some hiccups here and there.
Over this is a great game and if you own a DS and like adventure games then you must play this at least once. It's worth the 20 bucks for sure. Also if you like this game there is a sequel called Zero's Escape: Virtues Last Reward for the PSP Vita and the 3DS. Sadly, I don't own either one so I can't speak for the sequel.