This is a fun game. Combining the fuel, hp and currency together creates a really interesting interpretation of the theme. You can't spend everything you have at once or you will start the round with too little health. The art and audio fits each other too.
Here's some feedback:
- There isn't any benefit for destroying enemies.
- The movement doesn't feel natural. I'm not sure what type of movement you are going for here, but I think changing the velocity of the player to the direction it's pointing is not the right way to go. When you are traveling upwards, changing the player's direction without pressing 'w' should still make the player travel upwards.
- The controls and the pacing of the game can be improved. I rarely play games with this type of movement, but I think that the combat is usually slower paced so that the player can react in time and move to a safe position.
- Sound effects are too loud.
Great job on the game!