A cool little game! The difficulty ramps up a bit slowly, but that's a fairly minor critique. Some unsolicited advice if you don't mind: When you release the arrow keys, the player always snaps back to the right. You can fix this by only rotating the sprite if there is player input. i.e
if( Input.GetAxis("Horizontal") != 0 || Input.GetAxis("Vertical") != 0 )
{
// Do rotation
}