This game has a lot of potential, and I like the simple art style!
However, defeating enemies isn't that rewarding because nothing really happens after doing so. I'd really like to see some sort of score system - that simple addition would make the game way more fun to play because it would motivate players to keep playing your game! If you want to go further, you can even add more sound effects and visual feedback!
This is definitively a step into the right direction. Keep up the great work!