I really like the concept of the gravity shift platformer, but countdown as theme feels really tacked on and to the games detriment. I think the game would be markedly more fun if the gravity shifts were player controlled rather than on a timer.
The art was awesome, especially the clouds on the title screen, the music was enjoyable, but maybe little busy to be on loop for the duration of the game. A lower tempo or less intense sound choices would really level it up a bit. The physics felt good, but perhaps a little bit more friction or deceleration intensity when the player releases a direction would help with overjumping the platforms.
I think this has a bunch of potential though, I'd super happily play a longer version without the countdown timer being linked to gravity shifts.