One of the failings of most “interactive art” compositions on iOS is that they don’t give you enough control to feel like you are driving the piece. If I can’t feel my interactions effecting the piece, then I may as well be a random number generator for all the composition cares. With an app like the previously mentioned Conform, this is used to great effect, because part of that piece is the feeling of losing control. Thicket does a excellent job of keeping the feeling of control. Though the overall arc of the pieces seem a bit fixed, the visual aspects respond instantly and you feel right on the cusp of in control of the audio.
FREE (more compositions unlockable by in-app purchase) iPhone or iPad