If you havr the Orange Box than Pass, if you are new to Portal take it in.
In Portal its your job as a test Subject to use the new portal device to solve and escape various "Tests". Containing a two hour campaign and 14 new Challange maps (20 in total) its a great way to promote the series to new gamers.
The story is simple. Use the entrance and Exit portals to escape simengly impossible tasks and evenually your escape from the test center, but i wont ruin the rest for you. Your tasks will include moving Crates onto buttons to open doors or moving energy balls into power outlets with said device.
The game is a very simple yet Very, Very funny and engaging. I spent hours playing the campaign straight through and unlocking high scores on the challange maps.
I suggest the game to any fan of Puzzles or the original game but i do suggest buying the Orange Box instead of this game, but if not its a good 1,600 points on Live Arcade.