This is absolutly amazing. I commend you not only on your dedication to art but your fine eye for detail, creativity in use of a medium that most would probably not have thought of for such a progect, and the majestic simplicity of your overall design.
I can't decide if I'd like this as a print or as a tattoo.
I am absolutely amazed by your collage style! it reminds me partially of retro posters and their very simple style. as for the potato you might include "it" after a few weeks has past and nobody will be shocked by the potential spoiler : )
Given that Portal is largely defined by its bright, flat, smooth, clean and artificial surfaces and environments, the earthy immediacy and visual depth of physical materials that you use here is a very striking contrast; the art-&-crafts element also grants a light-hearted, whimsical, leisurely touch to remind us that Portal is ultimately a comedy!