Because of the side scrolling nature of the UI you've got some content on the right side that isn't relevant to what you're doing right now. (It takes away from what you're doing.)
The UI appears to lack any boundaries, rather relying on typography. It's interesting. I don't know how I feel about it, I'll reserve that kind of thing for the experts. It's certainly refreshing.
I see they've also created depth by having certain object scroll slower (or less.) Further removing the boundaries. (By boundaries I mean gradients, lines, blocks and buttons - I believe these objects give a UI a form of tactility?)