Great take on the limitation, I liked even the way the menu is displayed. The game is fun to play, the smash turbo makes a great contrast with the slow regular speed, making you take risks (as to collide with a not-so-open portal).
As a constructive critic, I would add some spacy soundtrack, playing as a background. And I had some trouble finding the green window-of-oportunity of the portals, maybe it could be less narrow, or more clearly displayed?
In summary, very good work :)