This took me a lot of trial and error because of the Game Mechanics not being self-explanatory at all... The score counter only displays up to six digits. You can have an unlimited number of lives but only a maximum of eight will be shown on-screen and as a result, I no longer knew how many lives I had. This made the process of trying to reach the game over screen really exhausting. Even though there's a bit of a difficulty curve at the beginning, it doesn't really get harder later on and the only threat are those homing projectiles coming from the aliens which are hard to hit because of both their speed and the fact, that you can only shoot in the direction you walk. I know you only added touch control and integrated the sore system, so you probably don't have a good overview over the code, but you might want to try and fix these issues. Anyways, as for mobile controls, I recommend on-screen directional buttons in combination with a virtual joystick for this type of game.
simple and cute ;-)
A bit unplayable on phone