Good concept and artwork. Movement feels really viscous and the spark mechanic works a bit buggy (i cant recall it sometimes). Platformer movement issues are a common thing in unity try chaning sensitivity and snap values for Horizontal axis in Input Axis settings or just check for pressed keys directly. For jumping I suggest this video. Also you can take a look at a game featuring similar mechanic. Good luck :)

I'm really just having a lot of trouble making any progress in this game at all.

Edit: Oh wait, there's double jump, I spent 10 minutes at the beginning of the game just jumping back and forth and throwing the ball around.

Edit2: Stuck again at the door.  Artwork's really good though, and the mechanic's neat, though it does get a little frustrating on the moving platforms because by the time you jump they've changed position since when you could see them.