A couple things makes my brows raise concerning the Microsoft headset.
1) The lower stated spec. The lower spec is only for none games, or lower tear apps. To use the headset the GPU still has to create two renders of the game in order to display on both screens. With this headsets higher resolution this means it will actually have a higher requirement then either the OR or VIVE. This makes its lower stated spec only applicable to none gamers or more casual gamer types.
2) It has not been shown to play a real game, only a simple home built app and video content. Microsoft owns Minecraft VR (by accounts a very cool VR game), why was it not shown with one of Microsoft's flag ship games? The Hololens was demo'ed with Minecraft and looked amazing, I mean who has not dreamed of playing this...
http://i.imgur.com/jCPcZKs.gif
on their own table. So why was the "Mixed Reality Headset" not shown with it?
3) No integration with the xbox one. This seems like a prime candidate to be paired with the Xbox, so why is it not?
4) Microsoft is not known for its first party games. There is a reason the xbox one arguably losing this console war and it is because of exclusive games.
5) I don't think its motion tracking will be as accurate as the others (just personal opinion as my work involves computer vision, and I see some compromises with their setup). I expect some compromises in order to simplify it. Might be very noticeable or could be nothing.
All this leads me to think the headset is aimed at a more causal market, those looking to watch 3D video and images and perhaps some light game apps. It will defiantly be interesting to see how it turns out. The more VR the better.