Coloruid

Coloruid is a pretty interesting game.

When you get to level three, it seems impossible and you want to give up. But if you fight just hard enough, you can figure out how it works and then finish the remaining 13 levels soon after.

I suspect that about 70% of the people who play this game don't make it to level 4, but of those who do, most of them probably make it all the way through to the end. A fun diversion.