This interactive gameplay video for XCOM: Enemy Unknown isn't quite a demo, and it's not quite a trailer. It's sort of like a choose your own adventure tutorial, letting you make simple decisions about squad management and tactics. And like a choose your own adventure book, if you flip through it afterward, you can see some choices that might have been.
It also teaches one very valuable, easy-to-forget lesson about XCOM: just don't take cover behind a burning car. That does not end well, because you will forget to move your guy when you know you're supposed to, and then the turn will end, and your guy will explode. And yes, I did learn that the hard way. Don't be like me.