If it weren't for the badges, I would've quit after about level 5. There is little reward for skill, it's almost all based on how much time you're willing to grind on it.
I was all for this game. And then I fought the same bosses a second time. And I was a little less enthusiastic. Then I fought some bosses for the third time. And the money I was earning wasn't enough to buy much of anything. This game easily could have ended after the first set of levels, and definitely should have ended after the second set.
I was all for this game until the last level. I flew threw 1-12 no problem, beating them on the first or second try. It was fun. I hit the last level and had to grind. No classic shmup requires grinding. There is a reason for this. Playing the same level over and over collecting money to buy a new weapon that doesn't change the game at all is not rewarding in the least. More and more flash games are adding length by requiring grinding, and this is one of the worst applications of that.