Portal is a first-person puzzle-platformer by Valve for PC, Xbox 360, and PS3. It was originally bundled with The Orange Box upon release.
Chell is challenged by GLaDOS, an artificial intelligence (Genetic Lifeform and Disk Operating System), to complete puzzles in the Aperture Science Enrichment Center using a portal gun with the promise of cake upon completion.
Portal offers unique gameplay and GLaDOS' dark, dry humor is brilliant. The portal gun is used by creating inter-spatial portals (orange & blue) between two flat planes in order to solve the puzzles. It is amazing, fun, and quite challenging. The test chambers vary in terms of hazards, so be prepared to die--a lot. There are challenge maps and two additional modes are unlocked once the game is completed.
Valve never anticipated Portal would be such a hit with players and was originally a mod for Half Life 2.