This is basically what a number of episodic games do - for example, the Ace Attorney iOS ports and the iOS versions of the assorted Telltale Games series. You c

This is basically what a number of episodic games do - for example, the Ace Attorney iOS ports and the iOS versions of the assorted Telltale Games series. You can download the app for free and access the first 1/5th or so of the game, and an in-app purchase unlocks the rest of the content.