Portal is a puzzle-like game based on the Source engine (Half life 2 etc), which is expected to ship with Half life 2 Episode 2. The game features around a gun known as the "Portal gun", you have to overcome obstacles and tricky situations. You fire first to set your destiantion portal, and the second for the portal to that destination. The game looks brilliant graphics wise, and a very interesting concept to be used for a whole game. An original idea which I think will be tons of fun.
http://youtube.com/player2.swf?video_id=GWzmL05OlYA&l=141&t=OEgsToPDskKpeSSxCt9RqzJHiLZERTvO&s=BDB533FA07002636:53C662DC848F75CD