What is Zero Escape!?
THE GREATEST SERIES EVER
But seriously, it's a hybrid escape the room / visual novel (although this one will be cutscenes rather than the visual novel part). Started with 999 (9 Hours, 9 Persons, 9 Doors) on the DS, was followed by Virtue's Last Reward on the 3DS/Vita, and this is the conclusion (although this game actually happens chronologically between 999 and VLR). You don't need to have played 999 to enjoy VLR and I don't expect you to have needed to play VLR to enjoy ZTD, but you should play them all in their release order to understand a lot of the references (especially with the handful of characters who are recurring).