The real killer (or at least differentiating) feature is that you can stream PC games from your desktop to the shield. Apparently it works pretty well[1].
[1] - http://www.theverge.com/2013/7/31/4573596/nvidia-shield-revi...
[1] - http://www.theverge.com/2013/7/31/4573596/nvidia-shield-revi...