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!
It was good and all, but it was kind of weird playing that way. The boss fight really sucked, because the AI was at my mercy as I lowered it into fire, and it was completely defenseless (not to mention it didn't speak throughout the course of the entire game)! So the boss fight was very anti-climactic and boring, and it wasn't much of a boss, just slowly lowering a defenseless AI without even knowing what is happening. It was also boring without any antagonist talking to me, but other than that, it's a terrific mod! I give it a solid 8/10.