We really liked it, reminds us of Warning Forever, but horizontally scrolling. The cards add a neat twist. Perhaps pickups would let you pick the good one. Or the bad one. I really hate orientation change, that messes with you. You should keep it, though we've wondered if orientation is always bad? Or is it that if it comes up good, it stays like it is?
The ending could use a tad bit more fanfare; I thought I died, but seems I've beaten the game like 10 times. Response in general, I'd have liked to more easily notice when I'm hitting the enemy and when my bullets are just out of range.
I wish it had more levels, maybe the boss could get smaller and smaller and angrier.
HP bar I don't think is necessary if you were to implement injuries on the player and let us interpret the HP off the sprite.
And the song does slap. :)