I like the concept idea, where less time spends on a level makes the power-ups more on the next one. It's like giving the player to be quick and fast while trying to stay alive, or risking to stay at one place and collect all of the power-ups. The shooting mechanic is annoying; I can't shoot properly to a certain position, especially when I'm moving. I wish there would be a way to skip the tutorial instead of following it all over again, both for the normal and challenging mode. Everything else is fine. Good job!