HoloLens looks like a very interesting product and The Verge has a pretty decent description of the potential of it:
you look down at the coffee table and there's a castle sitting right on the damn thing. It's not shimmery, but it's not quite real, either. It's just sitting there, perfectly flat on the table, reacting in space to your head movements. It's nearly as lifelike as the actual table, and there's no lag at all. The castle is there. It's simply magic.
HoloLens is still vapour-ware at this stage but it reality comes close to what they are showing, this could be a game-changer.