Negotiate a whole new plethora of physics puzzles in the world of portal. Traverse a non-linear map which has many paths that may be taken, and many puzzles that must be solved.
Aperture : Déjà vu
It is a non-linear map which have many paths to take and reach the end. The point is, that you play a map one time and you are happy. Then you have a little break in Portal, because there aren't any new released maps for some time. But the answer is here: play the Deja-Vu again, but choose a different path with different puzzles. You can choose freely the way that is going to lead you to the end. Thats it!