Art, gameplay and soundtrack very well set in for the mood of Portal, or what it would be like if it was made for the GameBoy!
I would maybe add a way for the player to reset the test chamber, in case the Companion Cube gets stuck.
I can see you thought on something of the kind because you have that 'chamber selection' screen working already. But maybe add a way to link the player there without full reset
Kudos!