Even though all of the gameplay features are finished, there are 44 levels. If you reach 44th level the game will be saved so you'll be able to continue from that spot when final version gets released.
"Invader Attack 2 is a shoot ’em up sequel developed by the one-man team at Codergames. Developed for PC, Invader Attack 2 is meant to offer a serious challenge, drawing it’s inspiration from classic, arcade-style games."
This is a trailer for the upcoming Invader Attack 2 (IA2) game that is still being developed intensely. It's due to be released by September 2014. Developer thinks he managed to finish between 70 and 80 percent of the game by now. While it may seem that there's not much left to be done it's quite the contrary as most of the bosses are not finished, they're neither modeled, textured, animated nor programmed.
Hm, I removed the tag but it still shows below the story. And can't remove it from the global list either.