It is not often that visual novels with legitimate, incontrovertible gameplay come out. It is even less often that they offer open-ended gameplay. InvertMouse’s Bermuda offers both.
Successfully Kickstarted for a measly $4060 AUD back in June, Bermuda is a visual novel featuring open-ended stealth missions. The game is about a group of friends who are abducted by an alien submarine while on a camping trip. It is broken up into six episodes, each with its own stealth mission, and the Kickstarter says that it was aiming to be about an hour or two in length. It should also be noted that the game is fully voiced over by professional voice actors, such as Cristina Vee of Madoka Magica fame and Kyle Hebert of Dragonball fame.
If the length does not deter you, you can get the game through the Humble Widget on the official site for $7.99. If you would like to try before you buy, there is also a demo available.