Thanks for the positive feedback. It was difficult finding a good balance, but you're right it's meant to be a little difficult, otherwise you'll get bored a lot quicker if you can get really high scores in your first go or two. There's a simple little algorithm/formula that increases the difficulty the longer you last in a single game. The gap between each missile launch gets shorter and shorter, but you're unlikely to really notice a difference until you're probably a minute or two into the game.