Just had my hands on and it is awesome!
Lets get the negatives out the way, field of vision of the projections is limited, but you get used to that after a few minutes, your brain adapts, and the colours are a bit washed out around light sources, we got to try it in a darkened room with a couple of artificial light sources.
But none of that matters because the thing is frickin awesome to use :)
The tracking is *rock* steady, its so stable, once you place something, it's glued in place, there is no jitter. you can walk around it, through it; the hand gestures come naturally, speech recognition is good.
The thing that will make or break this are the apps, its going to need a whole new mind set to write apps for this!
The best bit was the last task I had to do involved an X-Wing fighter that I had hanging in the middle of the room, that I could walk around and interact with. When I took the hololens off, I caught my self doing a double take when I looked over to where it had been, it seemed wrong that that it wasn't there any more, my brain had just accepted that it was a real thing in the real world and it was wrong that it had vanished!
You can't compare it to the oculus VR or the like, it's something different.