I just finished playing through a bunch of the demos in "The Lab" produced by Valve. Here are the salient things that stick out:
-The very first environment where you are standing on the top of a mountain on a gorgeous day in Washington (my home state!) is fantastic. I would say it is 90% there in terms of immersion. The textures are nearly perfect. It needs more ambient sounds (wildlife and wind). The teleportation system was almost perfect, though if you stand on the bottom portion of the cliff, you can't easily teleport your way back up the cliff because you don't have line of sight. I think the teleporting and visuals was the most remarkable aspect of this experience.
-Vortex Game: Your hand controller is a space ship and you shoot lasers. pew pew pew! you have to avoid little droids and their projectiles and lasers by moving your hand around. The screen gets chaotic pretty quickly. Somehow, I managed to beat the game on the first try. The interesting take away from this is that it's easy to forget where your hand is located spatially, so you can get shot from behind if you're not careful. The other interesting note is that it is very easy to dodge anything if you put your hand up close to your eyes and just use your eyes and body position to dodge stuff. This spatial positioning advantage is worth considering carefully for game designers.
-Slingshot: The voice overs and narrative were the best part of this game demo. Also, it's a lot of fun to catapult projectiles at exploding barrels. This was a near perfect game.
-The Lab: Of all the things they did, the one thing that was the most striking was their implementation of the dry erase board. You can grab the eraser and wipe the board, and the eraser position and orientation is line traced from its prior position to the motion controller position, and then placed on the impact point. This is exactly how you need to do all hand interactions with objects in VR. However, I think they messed up a bit with the markers because you can't control what angle you hold the marker at when you go to draw on the board -- they set it to a preset angle rather than using the angle you picked it up.
-Longbow: This is an archery styled tower defense type game. You are the one and only tower and you have to shoot hordes of paper cutout characters by drawing back a bow and shooting arrows at them. Each killed character emits two red balloons for body shots, three for head shots. Shooting balloons restores the 'health' of your gate. Shooting arrows with a bow is really fun. They almost did it perfectly. They've got a little bit of vibration feedback when you pull back the bow, and aiming it feels pretty solid. However, I think the arrow velocities need to be tweaked slightly. The biggest glaring problem with this however, is that my arms got tired very quickly! This became a huge problem, to the point where I had to consciously decide NOT to shoot at balloons because it would tire my arms, and I'd rather reserve my strength for shooting at the invaders. This means I had to start making physical fatigue management an important game play consideration. I tried alternating between putting arrows in my draw string and pulling them back and putting arrows in the draw string and pushing my bow forward. I think the most salient point here is that your VR games shouldn't have repetitive motions which involve players holding their arms out for long periods of time. You'll want to alternate the types of hand motions players use so that the diversity of arm use doesn't fatigue them quickly.
-Robot Repair: I've demoed this one many times, and its fun every time, though not very replayable. The interesting thing here is the sense of presence you get. I'd say they pretty much nailed it. You don't want to walk through walls or tables, or robots because they feel so real. Just for fun, I walked through the walls in the game. They let you do that, and it feels weird to clip through them. I think its a slight design problem, but probably not too big of a deal. One other thing I noticed is that when I was examining the holographic portion of the robot, it's holographic lines exactly matched the color of the lines of the 'steam chaperon' boundaries and I accidentally walked into a bookshelf not realizing i hit the borders of my play space. This brings up an interesting point which game designers can consider: play space management. If the player strays too far, you can pause the game and assist the player in returning to the center of the action. I think this might be the only permissible time to intentionally break immersion because player safety is a higher concern.