I'm a fan of "digging" games, and I like the twist this adds of having to manage inventory. While a very different game, it reminds me a bit of the arcade game Rampart which alternated between block placement and action, with the block placement seeming odd at first, but actually turning out to work well. Really original and fun idea!
The only thing I didn't like as much was the controls. I really wanted to be able to right click to rotate instead of using R.