This game has a lot of potential, the idea is great, however I think that you can improve this by adding some things :
1. Add a button to restart without passing by the pause menu.
2. Remove the timer, and made the game stop when the player cannot win any longer. I know that is certainly a tricky part, but it could be a great improvement.
3. Add a puzzle mode when you can choose and try any level. Keep the actual mode as the "arcade mode", but if you have a lot of level it could be great to select it.
4. Add a level editor. This game is made for a level editor. Plus it could help you while your creating your own levels.