Hi! Thanks for your feedback and support :D
You're right, the game needs some info about controls. Maybe a panel showing the controls mapping would help.
I'm avoiding checkpoints that make the player to return to a previous point. Right now, when the player is destroyed it is immediately spawned on the left side of the screen and the shield is turned on. This way the ship doesn't collide with anything for a few seconds and the user can avoid the ship to get stuck while the shield is on. Probably it's not the best and obvious way to respawn the ship... I'll look into it, thanks for pointing that out.