I don't know how the hololens screen projection system works. I suspect that they have three very thin layers of glass and each layer contains the red, green and blue channel and they rely on the additive properties of light to render a colored image.
Rendering an imagine is the first of many big challenges you'd face if you're going to make your own AR device. Remember that augmented reality is... augmenting reality! That means you have to know a bunch of things about reality before you can augment it! You need to know where things are in reality space, so that means you'll need to have two cameras that are constantly doing image capture, feeding the capture to a processor, which then tries to gather depth information to create a "z-buffer" for the real world. Why do you need this? For occlusion of course. If you have a ball in augmented reality and it rolls behind the couch, your device will have to know that the 3D position of the ball isn't visible anymore because it is being occluded by the couch. But, maybe a portion of the ball is still visible? So you'd have to do some fancy logic against each pixel in the ball mesh to see if its depth buffer test is less than or greater than the real world depth buffer. Then you've also got to map out the shape of the objects in the real world so that you can have collisions with it. Your ball should bounce off of the couch rather than phasing right through it, and in order for that to happen, you have to do some time processing the environment around you in order to generate triangulated collision meshes.
This is computationally expensive stuff, so the "magic" of the hololens is that you're really wearing a stand alone computer on your head which has enough processing power and battery life to do this decently for a reasonable amount of time. It's really quite incredible if you think about how much computational power you'd need to do this, and they've shrunk it down to the size of a head band. You also have a microphone, so you can issue voice commands to the system which is pretty smart at interpreting them (I've never tried that feature).
Anyways, trying to compare hololens to oculus rift is like comparing boats vs cars and complaining that your boat can't drive on the highway, or your car doesn't float. They are fundamentally very different...