The launch trailer for XCOM: Enemy Unknown, subtitled "Our Last Hope," offers a look at gameplay to celebrate next week's release of Firaxis' continuation of the X-COM series of sci-fi strategy/action games. They say: "Take command of XCOM headquarters, recruit and train your soldiers, and research alien technology to advance the capabilities of your squad. The battle against the enemy will be tough, and success will depend on your ability to keep your recruits alive and evolve them from rookies to more skilled and powerful soldiers. You are our last hope to save humanity from the global alien invasion. Good luck, Commander."
They said something in an interview somewhere that there are a decent amount of maps and that in one playthrough, which usually last 30 missions or so, that you would not see the same map twice and that each map has random starting points so it'll be a little different as you move through a game. I think all the starting positions for everything are random every time.