bbc micro:bit: FULL Space invaders

Got a few requests to make the full game of space invaders. i thought id meet them half way with an alien shooting at the player and you shooting back.
While creating the video i had a thought of the game being over too quick if the alien dropped down given the game would be over in 4 drops AND the fact you can time the bullets perfect, didnt seem like much of a game. Please respond with that type of game, ive tried to do something a little more challenging.