You and your colleagues are experimenting with interdimensional teleportation technology. The demo was meant to deliver the experience of Half-life without ruining the story line, yet showing off all the aspects that made the full game such a blast to play. And I must say that the demo is every bit as good as the full featured title. The first big change that you will notice is the look of the game. Bullets leave marks on the walls, missiles leave smoke trails and burn marks and heavy water gives off incredible smooth glow.
Weapons are also well done, they are precise and beefy.
You almost feel how much lead you pump out your machine gun. Sound is another big part of the game. You hear marine radio chatter as they hunt you down and alien howls send a chill down your spine. Hellish creatures actually ambush you. The first time I encountered Marines, I popped around the corner for a fast peek and noticed 2 of them kneeled and ready to fire.