I'd emphatically recommend Zen Bound and Zen Bound 2.

More than most other mobile games with good touch controls, the Zen Bound games really took advantage of the tactile nature of current mobile devices and their touch interfaces.

Aside from the mechanics, they were also pretty relaxing, while some of the levels managed to be simultaneously challenging while remaining completely passive. A very gentle and non-frustrating form of challenging that not many games manage to achieve.

I don't think Zen Bound gets enough praise as a game that is unique both from a gameplay perspective and how well it relies on the interface of the underlying device.