Best Wii U eshop title (that's not sold at retail)

[d21lewis]

I have: Trine 2, The Cave, Little Inferno, Mighty Switch Force 1 and 2.

I might be forgetting something. Anyway, I have $20 on my eShop ID for use between Wii U and 3DS and I want something new to buy. Any games that take advantage of the pad in a meaningful way?