Here’s a clip from ‘Portal’, a game by Valve. The full review with the list of game's achievements is available at

The game is built around a gun that shoots teleport portals. You can shoot to place a portal on a wall, ceiling, floor, under an object, etc. then shoot again to place the other opening to the portal.

This. Looks. So. Cool.

Portal looks to be a single player game that stresses puzzle-solving. GameSpy is reporting that it will ship with Half-Life 2: Episode 2.