Yeah, you need to be able to lock things that you know are set right, and there isn't enough variation to make 50 levels interesting. Still, it's oddly addicting...
Here's some tips for #6 and the whole game...
When you've only got one pellet, get a big one by itself, shoot it, and then pick up the pellet and shoot it again. Keep doing this until you whittle one down to more pellets. Once you've got a few pellets, get them all stacked on one side of your UFO, and shoot another big orb; each of the pellets you hit it with will split it again. Also, don't be afraid to lose a little life chasing down pellets; you only need to live through the challenge.
The challenges are great; like a boot camp for the game. Pretty good difficulty curve, and learning how to play fast makes it pretty easy to get past the first levels quickly. Gets old after a while, though. Could use more powerups.
Really fun concept, but the problem with all shooters nowadays is the redundancy of weapon choices. It's always the same. I did like how you added different kinds of upgrades for certain weapons, though.
The clicking around gets annoying when you don't really have any idea what you're trying to do, especially in the traffic scene. Also, it seems odd that you're supposed to kill people twice. But great art and sound.
It's like a vacation from your mind. So soothing. The only thing I'm wondering is whether or not it's possible to hear an aberration in the music when a special color is coming out. Other than that, the only other comment I have is Purple Power!
I beat 36 waves and felt like quitting 20 ago. Loses it's touch after a while. Could also use some more diversity in weaponry than just your standard Thing-Thing variety.