I was able to use a head mounted (and tracking) 3d display with a computer back when ROTT was popular (circa 1994). It's a novelty at best, and a headache inducing nightmare at worst. I didn't see the magic then, and I certainly don't see the magic now.
A seamless hud, on the other hand, has the potential to do great things for your interaction with the environment. Based on reviews, however, it's still years out.
Actually, no, this one didn't. It was fantastic technology. The resolution was the same as the monitors on the other computers, and the tracking was very fast. The only downside to the technology itself was that it was heavy.
The problem was that it was only a window, and a relatively small window at that. It's a glorified 3d monitor that denies you vision of your surroundings (and works very poorly with anyone with glasses).
Worse? You still need some other sort of controller (which you can't see when you're wearing them), and unless you're standing up, you can only look a limited amount around you. In any environment other than wandering around a virtual world, it's a curiosity at best.
FPS games - the head moves too slowly to make an accurate method of aiming (and think of your neck muscles afterwards), so you still need to use a mouse as your primary aiming device, and a keyboard to move.
MMO games (perhaps the ideal target for these) require extensive use of the keyboard and mouse (neither of which you can see with the device on), and are rarely played in first person view.
I just can't really see a market outside of VR, and then not without a whole new class of controllers and tactile feedback methods. It's the first (and arguably the easiest) part of a new class of technology, which when combined could be interesting. Until then... meh.
The final one will have full HD, but even then I think it needs a quadrupling in res before it's even acceptable.
They're very different devices. The Rift immerses you in 3D worlds. Every way you tilt your head immediately changes your viewpoint. My perception of Glass is that it tries to overlay information on top of reality and add more senses to humans. They are similar means to completely different ends.