[spoiler] For those having a hard time finding endings, keep in mind that sometimes there's a third path. For example, in the first stage, hit X just enough to press up against the egg's wall.
Pay to Win much? There are plenty of commercial shooters that are better than this, without the requirement to keep spending money in order to be competitive.
It's not a game in the traditional sense, but it was produced for a tounge-in-cheek "game jam" based on the ideas tweeted by @petermolydeux. If you look it up it might make more sense to you :-)
Special is the most important thing, but missile will help speed up levels. There's no point in spamming specials, since only the lead one will attack.
The fastest wins come from strong armored special, strong shooter, missile missile missile etc.
Sadly its the nature of the free-to-play business, in physical CCGs everybody has to pay.