First goes for the vision. The vision is superb, stating from an individual who never played Portal before. I didn't dock too much points off of originality, but due to the fact that I've seen several aspects of the pentool being used in that way, I felt it would be wrong to give the originality a 5.
I really love the pentool technique for the curves branching out from the 2 straight lines. I also loved the blending options to give the lines a glow to it. One of the best things about this image is the way it balances. While each element is balanced on the grid (especially the canvas), the colors balance out. Not saying it is a hard technique, it's just something to keep in mind of while critiquing.
The lighting isn't really my style, as I would've put a more darker appeal to it, enhancing the glow and the overall perspective of everything.
I would've tried a little gradient, not a strong one, but a weak one on the branching lines, just to see how it matches with the overall lighting.
Overall, simplistic, and yet superb when it comes down to the vision.