I got a fright when the tank produced a sound effect when shot at since everything is otherwise silent! Haha. Well done, the game is shaping up nicely.
I hope it's okay if I make some suggestions:
1. The enemies don't damage you. You could also make them knock the player back a bit if you put a move player relative -1 to x coordinate if facing right and +1 to x coordinate if facing left. That way, the player will feel the impact of a hit more (you could also try this out when the player gets hit by a horizontal projectile).
2. Consider putting more health in the level to help the player out. If you want to reward the player for being good, you can put a checkpoint in somewhere that checks if they have max health and give them a reward. Or you can rank them on completion of the level for example. Something like; if the player has max health then they get an A rank and so on (if you wanted to implement something more complex you could make a variable that tracks a score and increment it when the player kills an enemy. Then rank the player at the end based of the score). What extra health and a ranking system does is ensure beginner players dont have a frustrating time, and more experienced players have a good challenge on their hands!
You have built a strong foundation for a good game. Very well done!!