What next?
More games!!!
I hope that you don't think that any game you (or anybody else) develop will have the same luck. Probably 1 / 10,000 will get 400,000 downloads.
If you asked b4x members how many downloads they got you would be surprised, I think.
THE guru of LibGDX, with his game, got about 500 downloads!
The main reason for the success of your two apps is that Invaders has been a famous game for decades.
Probably even games like Pacman or Tetris have got the same success.