Nice game! I especially liked the level design and graphics a lot. Also the idea that you unlock the sections with the courage points is nice.
I found the game a bit hard and punishing though. The first two levels were relatively easy, but it took me some time to realize that you can hold space for higher jumps(even though that's for most platformers). Also it feels like the player decellerates too fast when letting go of the arrow keys. Maybe just a matter of preference though.
The 3rd and 4th levels were much harder though, and took me multiple tries to beat. I wouldn't mind trying them multiple times but resetting the whole game because you die is boring, since the first two levels are so easy. After half and hour I managed to reach the bossfight but died, and can't bring myself to play through the whole game again.
So in conclusion the single improvement for this game imho is to add checkpoints when you die before the level/courage sections of the game. Everything else was superb though! So much attention to detail, like having the turrets indicate when they fire, or the character looking happy when collecting courage shard. I enjoyed the game very much!