I’m really quite impressed with this game. I’ve managed about 12 stages so far, with Million Invaders being the most taxing. There are about four times as many invaders as usual, all 1/4 of the size. It takes quite a while to kill them all, plus you’ve got more to shoot at you!
I found out that getting hiscores on Original mode also unlocks power-ups for New Age mode, so I played that for a bit too. And only managed some 1,800 points. It did unlock “Speed Up” though.