Keep playing to unlock upgraded ships that can boost, shoot, or use force fields.
For those of you who are bothered by having to click the play button each time, you can push ENTER for rapid-replay action.
Still trying to get the difficulty right, it is much easier to unlock a shooting ship now (you only need to get 2k points); and the game starts out easier & becomes progressively more difficult.
Thank you for the comments :)
btw, you refill your missiles when you collect hp boxes