Looks good! I'm familiar with the Impossible Game (although I've never played it), so I noticed the reference right away.
edit2: I also haven't gotten around to making a bigger map since it's really tedious placing the boxes at good locations. I need to make a level editor i think.
How are you making the map right now? Manually placing the boxes in code? Reading a file?
I'm manually creating them in the game constructor right now. I'm not using tiles or anything like that. A typical box creation would look something like this:
GameRectObject *box = new GameRectObject(PhysicsType::staticT, *_physicsSystem.timeToSimulate(), 3500, 500, 50, 50, Flag::fallsWhenTouched);
_physicsSystem.addItem(*box);