Microsoft's HoloLens provides a unique AR experience in several ways.
The user is not blocked off from the real world; they can still see the world around them (other people, desks, chairs, and so on) through the HMD's semitransparent optics.
The HoloLens scans the user's environment and creates a 3D representation of that space. This allows the Holograms from the HoloLens to interact with objects in the room. Holographic characters can sit on couches in the room, fish can avoid table legs, screens can be placed on walls in the room, and so on.
The system is completely wireless. It's the only commercially available positional tracking device that is wireless. The computer is built into HMD with the processing power that sits in between ...