The reason why 3D doesn't work is that it is not 3D. Instead it is some strange kind of 2.5D where you have what is essentially a topologically 2D manifold embe

The reason why 3D doesn't work is that it is not 3D. Instead it is some strange kind of 2.5D where you have what is essentially a topologically 2D manifold embedded in 3D space. This means that you cannot look around things, or change occlusion by moving your head around. As others have mentioned, you also cannot change your focus. Until 3D becomes actual 3D, it will always ring hollow. It's possible that Oculus may be the platform that achieves true 3D, but I suspect until we arrive at a place where the "holodeck" is a fully functional universe, we won't get there.