I agree with PikonParadox, main thing I noticed off the bat was bullets and no plane, which although is a good indicator seems unfair and not something skill can help you with. I would suggest maybe a flashing indicator instead and then have firing start when within range. I found I wanted to drive my tank but I understand this probably intended for your game. 

The movement of the planes was challenging, but at the same time didn't feel so much like planes and more like helicopters (rotating around you).

Great start and fun jam submission. 

Nice concept, roughly decent execution. I liked that the planes randomly switched directions. It added a bit of a challenge. 

Few suggestions that come to mind are-

1. Let the planes shoot only after they are visible in the screen.

2. Start the game with slower airplanes. gradually increase the difficulty. (You could also assign specific behaviour patterns to each type of plane, kinda like the ghosts in Pacman)

3. Reduce the frequency at which the planes are firing, at least for some of the planes. If possible, you could add dynamic difficulty where they shoot fewer bullets when the player has lower health.

4. Add power ups where if you shoot certain types of planes, you get specific type of bullets or abilities. (or implement the power ups in some other way that you think works)

Overall, it's a nice game and has good potential. Nice work!

Fun game dont think the base should rotate if you are stuck other than it was fun nice