Well imo, Shield is a far different device than Ouya/Gamestick to make any comparisons.
It's supposed to be a handheld console which can also stream from your PC.
In that aspect it kind of draws near what the Wii U gamepad is/does, whereas Ouya and Gamestick require a monitor to be plugged in and follow more a "living-room console" architecture.
Ouya and GS are likely to be portable, but will still require a screen in which to plug in, whereas the Shield is supposed to suffice itself and also has a monitor output.
I'm excited at the idea of streaming my HTML5 game executed on the PC on a portable console (not a tablet or phone).
As for the design, I find it kind of old school and it really makes me think about a portable xBox/gaming machine.
Anyway, it's early and it will depend on the price to see what market share the device is supposed to fill.
I still feel more excited about the Shield than the Ouya/GS.