Cool game, though I do have a few complaints:
1) I feel like the player's sprite should be inverted based on the direction they're moving, not the direction of the mouse cursor, seeing as the mouse is barely used.
2) The tileset was a little wacky occasionally, like when platforms would jut out of a wall, they look a little off to me.
3) There were many areas in the game where the tileset wouldn't cover the full screen and I'd be able to see the background outside of the map (make sure you play test with the full resolution?).
4) I didn't really get the On/Off concept much, except for the 2 times in the entire game when you would activate something. Am I missing something?
5) The player controller felt wacky to me especially when moving in the air. Also, you can jump on the side of blocks and also get stuck sometimes on the side of blocks. Nothing too bad but it was a little weird.
Other than that, great job! The art was nice, the sfx/music were great, and the atmosphere was well done. With a little more polish, I'd be excited to see where this goes next!