Good concept, but the gameplay is a little repetitive. I also found the rate of decay for the timeshield to be a little bit pesky. Instead of -10% until 10% then -5% at 10% then -4% at 5%, you might want to make the rate of decay -1% after 5%. The game gets quite a bit boring at 1% because of how slow it runs, but a slower decay rate would fix this. This game could also use something to make the player want to play more, such as upgrades, such as more controlled speed or more damage, or even something like explosive missiles. Still, not at all bad for your first game.