Not really worth it
The first 2 levels were nice and easy, then level 3 got a bit harder and level 4 was just insanely ridiculous. The ammount of enemy bullets is just impossible to dodge because they basically fill the whole screen and the weapon upgrades don't really do that much damage.
Almost a good game...
Until you get to the last level, which is so impossible with so much shit going on its not only absurd, its downright annoying. If you're gonna have 6 thousand enemies on the screen at once you should be able to upgrade to a point where you can actually stand a chance.