aXes

Nice concept, you could develop this and make it into a full-length game!

I have some ideas

1) Disappearing blocks

When you touch them, they fade away

2) Buttons

By standing on it, it would open a gate.

3) Boxes

You could push boxes onto buttons, and change their gravity as well

4) Canons

Canons would shoot spikes in the direction they are facing, and the bullets would not be affected by gravity. I have an interesting puzzle idea: The cannon in this level would be shooting up, and so trying to pass would result in you falling on the bullets. To pass you would have to change gravity to go on the Z axis, so you can jump over the bullets.

I have some more ideas that would be helpful but it is possible you have already rejected them:

1) WS

I know that some of the puzzles rely on this not being a thing but... I think it would allow for more freedom and puzzle combinations to be able to move forward and back with WS

2) Camera Controls

This would allow you to change the direction of where the camera is facing, possibly with the mouse. Maybe also a camera reset button, which would be helpful for knowing which direction you would change your gravity in

Thanks, and I hope you enjoyed this feedback