If you're unable to download XCOM: Enemy Unknown's PC demo due to a Sectoid incursion of your higher mental functions, check out this YouTube-based choose your own adventure video.
The fork-in-the-road style video lets you choose what will happen to your squad on a routine mission to give planetary outsiders a ticket to XCOM HQ's autopsy slab. Don't worry if rookies die. Rookies always die.
If you're looking for a less interactive XCOM viewing experience, you can always check out the hour-long playthrough by the developers.