We have always wanted to play on the holodeck ever since we watched our first episode of Star Trek: The Next Generation. We know there's something pure about it, deep in the base of our spines. We want to be completely immersed in a world that doesn't actually exist, but is so real we believe it does.
Currently, when we play a game we can enjoy it for what it is, but there is always that separation between the game world and ours. We still know we're dealing with a mouse and keyboard, and we don't really exist inside of the world - simply viewing it through a screen and several layers of garbage if your desk looks anything like mine, which is kind of a let down if you're playing the next installment of Leisure Suit Larry: Look! A Game With Boobies.
It won't be until technology improves - or becomes more affordable - that games will be able to really immerse us and create an atmosphere like the holodeck. Nintendo is the first company to take a real stab at this by introducing their Wii, and more specifically the remote. Instead of being something with which you interact to indirectly control your avatar, the remote allows you to become the avatar. A game like Wii Sports allows you to not only control a representation of yourself, but to be yourself in the game. It immerses you in a world that isn't yours.
But motion sensors are not enough to fully immerse. What you really need is a much larger screen; much larger, as in completely three-dimensional. As the screens get flatter, lighter, larger and cheaper, a 360-degree "screen" isn't far away. With built-in sensors, you could put screens around the player and remove external controls from the process. The idea that we are anywhere but the game world slowly starts to melt away when you cannot turn away from the screen at all.
Once you have the visuals down, you can easily incorporate surround sound. When you're standing in the middle of the world, 3-D sound will be crucial to intelligent game designers. As it stands now, you can't really rely on it to get the player's attention, but if surround sound is a given, and it's well on its way to being so, sound goes from a value add to a significant gameplay component. Imagine slowly moving through a destroyed city, and that city is actually all around you, you can see it in your peripheral vision and everything, and then you hear a sound come from behind you and slightly to the right. You turn around to see what it is, and if a crazy kung fu fight ensues, all the better. Just make sure you stretch first.