If you're sceptical about Oculus Rift, here's an experiment for you. Download Doom and play it back-to-back with a modern FPS. What you'll probably notice most isn't the low resolution or the weird cardboard-cutout objects, but the absence of freelook. You'll find yourself jarring as you try to look up at ledges or peek down through windows, feeling peculiarly constrained, almost as if you're wearing a neck brace. The Rift is at least as big a difference.

HMDs with accurate head tracking are an absolute revelation, because they truly immerse you in the environment. You don't realise how much your natural vision relies upon your ability to take quick glances at odd angles - a look down at your feet to spot the last step, a peek over your shoulder before you merge into traffic and so on.