Not a bad game
It's obvious you put some effort into this. First of all make the buttons you click on actual solid buttons so I don't have to reposition the mouse a little to click on a button. Second you should have some kind of score system where harder levels give you more points, so completing a level isn't so pointless. Or what you might want to do is make the game progressive, where it starts you out on mission 1 and you have a certain amount of lives, and then you go to mission 2, and so on as you complete the missions.