I like how the mechanic that you control two characters at once reminds me of Brothers: A Tale of Two Sons. I believe that the idea is there you just need to up its potential.
As a platformer game this needs precise and tight controls, for me you nailed the movement speed and the ability to control your character mid air. The problem lies with your jumping mechanic, there is no right or wrong value for the jump height you just need to tune it until it feels right, this also affects the placement of your platforms which is the foundation of your levels so it is very important to improve on.
The game is actually very straightforward which makes it a good thing since depth is more important than complexity. You can actually add more depth to your game by giving each your characters their own personality. A very good example of this is weakness and strenght, you can have the other one slow speed but have high jump height and the other one faster but shorter jump. Or by giving a means of interaction between the two characters.
Overall you did a good job making the game. Continue to strive and improve upon your creation and skills alike. Congratulations! =)