2D Space Shooter thingy - (Not) my first game

Your objective is to destroy all the incoming asteroids. They come in waves, each wave being separated from the next by a few seconds.
You start the game with 3 Hit Points (HP), every collision with an asteroid will take you 1 HP (no matter its size), and if your HP reaches 0 it’s game over.

Destroying asteroids will earn you points, and you’ll lose some for each asteroids that reaches the bottom of the screen (it won’t affect your HP). Each time you survive 5 waves in a row without taking a single hit, a bonus will appear at the top : picking it up will increase your HP (not capped at 3, you can get as many as you want). It doesn’t matter if asteroids reach the bottom of the play zone in the meantime, as long as you don’t receive damage for 5 waves a bonus will spawn.

The game never ends, unless you die of course, so aim for a high score !  But the longer you play, the harder it gets.

When the game ends, you can restart by pressing the “R” key. Keep in mind there's no feature to save high scores. I'll learn to do that on my next games.

CONTROLS

• Use the arrow keys ←↑↓→ to move your spaceship.
• Use the key “X” to shoot normal shots.
• Press both the “X” and “C” keys to shoot in “focus” mode. In focus mode you shoot a lot faster and way more precisely but your ship will move slower.

I do not think of this as my first game, as it is strongly based on Unity's official tutorial. You can learn more about the "WHYs and HOWs" on this dedicated post on my blog.