Portal is one of those games that you absolutely need to play if you consider yourself any sort of a gamer.
In Portal you play a silent protagonist who is, for some unknown reason, put through a series of tests using an experimental portal creating device, the Aperture Science Handheld Portal Device. You are guided through these tests by an A.I. going by the name of GLaDOS, who may or may not be telling the truth, which adds an interesting twist to the core gameplay elements. Though harmless at first the tests, contrary to GLaDOS's initial statements, become more and more deadly as the game progresses and players must rely on their own wit to make it through them alive.
The game is dripping with sophisticated black humor and while this is certainly an important aspect of the games overall quality, the real beauty lies in the solving of seemingly impossible puzzles with the portal device.
The function of the device is to create two distinct portals, one orange and one blue, and either can be used as entrance or exit. The puzzles you are presented with throughout the game are cleverly designed to allow you to use the device to overcome them through relatively simple means, thus making what at first seems impossible to be very possible. For example, in one of the testing chambers you are faced with the seemingly insurmountable odds of making it through a turret filled room, with each of the AI controlled weapons placed in highly strategic positions. This may seem difficult, but if you use a little brain power, you'll find out that overcoming it is incredibly simple.
As I said, this is Portal's greatest strength, it makes you think without ever becoming too frustrating and thus negating your enjoyment of the game. So many games these days rely on a tried and true run-and-gun method that can almost be played with your mind focused on anything else around you but the game itself. With Portal, Valve forces you to pay attention and use your own intelligence to make it through the game alive. The game even provides extra challenges such as timed test chambers for the those with quick minds and a mode that requires you to make it though in a specific amount of footfalls for those who wish to push the requirement of planning things out to the extreme.
While the game is relatively short, most will find that it's length is just right. One doesn't feel like they were short changed at the end, nor does the game ever over stay its welcome. In other words, the amount of hours you put into on your first run through is balanced out perfectly.
Valve has done gaming a service with this game. They've forced us to think while giving us a hilarious and refreshing experience that will live on in the minds of gamers for a very long time. Intelligence, solid gameplay, and fun. What more could you ask for in a game? Be warned though, the cake is a lie.