I was going to get a Ouya but considering that Nvidia just dropped the price on the Shield to $299 I will probably go for that rather
I think the Shield is an interesting piece of hardware (except for aesthetics). Console & portable gaming are a little different, so there is room for both (and comparing Android devices to Android devices is more of an "apples to apples" comparison than an android device to ps4). But it always comes down to games. I don't think anyone will make games specific to the Shield, and I already have a fancy android phone, so I can play android games on that.
The Ouya has a great business model. See for a few years people have been trying to get console quality gaming on mobile platforms to little avail, the Ouya has realized what people REALLY want to play is mobile quality games at HOME tied to a console with a controller! I'm super stoaked for this Ouya KILLER APP.