Let's get the unexciting stuff out of the way right now: Gear VR has an accelerometer and a gyrometer for tracking head movement. That means it only tracks where you're looking and not depth; if you move your head forward or backward in the real world, that movement isn't reflected in the virtual one. And that stinks.
When you turn your body all the way around and look behind where you're sitting (in the real world), and there are no wires stopping you from looking wherever you want, that is magical.
This duality is at the heart of Gear VR, but it applies to all mobile VR at the moment. No wires means better immersion, which is crucial for delivering the promise of "presence." No wires also means no dedicated video feed from an autonomous device (like a PlayStation 4 or a PC, for instance). While Sony tackles depth tracking with its PlayStation 4 camera and Oculus handles it with a camera peripheral of its own, Gear VR is dependent on the hardware in the phone and headset. That is both a benefit and a curse with current technology.
There is no "screen" -- Gear VR uses your Note 4 screen, which is of the 5.7-inch, Quad HD (2,560 x 1,440) Super AMOLED variety. It looks crisp, and the Cirque du Soleil video I watched was neat. When I turned quickly, I wasn't able to discern any major irregularities ("screen-tearing" or other nasty hitches). It's got a 96-degree field of view (just four shy of Oculus Rift's latest kit) and a 60Hz refresh rate. There's a square touchpad, a back button and a volume rocker on the right side of the headset; the touchpad is used for tap-based selecting, while the back button is both for exiting software and enabling pass-through video mode (both of which I'll get to in the next section).
Gear VR isn't very large (198 x 116 x 90mm), nor is it very heavy (exact specs aren't available), and I wasn't ever uncomfortable wearing it. The padding around the eyes can be replaced easily, which Namkung calls a necessity for longtime users.
Samsung's been working on the Gear VR for approximately 1.5 years now, and Namkung says some of the development units -- the ones we heard about so much back in May -- got a little rough around the edges after prolonged use.
Audio is handled by the Note 4, and it's of the "3D spatial sound" variety. That just means that it sounds like it's going to both of your ears despite the fact that it's coming out of the Note 4's non-stereo speaker setup. This actually works better than expected: Audio consistently sounded like it surrounded me, which makes the immersive experience all the better.