Ruben & Lullaby could be described as an art game. Also could be described as an amuzing, interactive art piece. As short as it is, and as limited as the replayability is, it's still a delight to play.
The story is that Ruben & Lullaby are young lovers who have just had their first fight. By your actions in guiding them through this argument, you can either break them up or patch things up. You have three main, simple controls - tilt the phone quickly to switch between the two characters. Shake the phone while touching the screen to make the current character mad. Stroke the screen to make them sad / remorseful.