X-Com demo was extremely disappointing. I've been looking forward to this game for a long time so that sucks.
5gb download gave two missions, one of which was completely scripted - you had to do what they told you to do. After, it told you what to choose for your character when they leveled.
The second mission gave you freedom to move around, but when you were done, you had no control over your characters leveling up, no build options in your base, no research, nothing. The demo ended and that was it. So basically, you got to see combat and nothing else, which is 1/4 the total game.