Fun and innovative puzzle game from creators of half-life.
As the title suggest, the main theme of the game revolves around the portal gun, on which you'll rely heavily as you make your way from one level to another. This might seem like very simple concept but creators of the game were creative enough in making puzzles so that you'll need to think hard how to use portals' properties to proceed to the next location. One of the disadvantages of the game is that it's pretty short: as a matter of fact you'll most likely be able to complete the game in one evening. Afterwards there are bonus maps unlocked that are considerably harder, but even with that extra content the game seems short.
At first I took Portal for another puzzle game where you can't die and friendly voice guides you and gives you tips... However, by the time I encountered machine guns I realized out that things are not what they seem. While the puzzles are the main theme of the game the plot gets interesting enough that you want to keep going.
As a small spoiler ( stop reading here if you don't want to find out) I'll add that you never get the cake you were promised. Instead, you get something else: a song. A song is much better because cake would have given you nothing but empty calories; but song will make you laugh so hard that you'll burn a bunch.