Interning at NVIDIA and I have one sitting on my desk right now.
The use of WiFi Direct in the controller is supposed to improve latency + throughput vs Bluetooth (about halves it by NVIDIA's claims... and at the same time it has a mic and headphone jack). But just like the original SHIELD you can pair any Bluetooth controller or a keyboard and mouse to it and it should just work (or you can use a USB OTG cable and a USB controller). The third party controller support in SHIELD is very good compared to most (if not all) Android devices.
If you compare this to a Retina iPad Mini, it's really not a bad deal - you can get the device, the controller, and a cover for the same price as the base iPad Mini. It has a lower resolution screen but a much more powerful CPU/GPU combo than the Apple A7 and comes with Gamestream which is useful if you have a recent NVIDIA GPU.
If you look at it purely from a tablet perspective, compared to the Nexus 7 (2013), it has a pen, a much faster chipset, a bigger screen, and close to stock Android for about $70 more. There's a tradeoff of price vs features here, but it's a tradeoff that I can see a lot of people making, even if they aren't interested in gaming on it.
I can probably start answering more questions about the device (specific things about the hardware/software itself that isn't public yet) when it ships on the 29th. I did order one for myself, though I'm probably a bit biased since I worked on it