I did notice some improvements and I hope you don't mind a few more notes.
- The speed of the ship was just a little too slow as compared to the original game.
- On levels 1 and 2, the invaders still moved too slow, but on level 3, they moved too fast. I don't believe that the original game had the overall speed increase as you progressed. I know that as the invaders drop to the bottom, they would speed up.
- The invaders now move all the way to the left, but as columns of them are cleared, the inner columns of invaders aren't moving all the way to the sides like they should. Basically if someone clears all of the leftmost invaders, you need to adjust the width of the surface the rest of them are attached to.
- The collision detection still needs work and the bases are still not being shot up by the player's ship, only the invaders.
Thanks for working on this and I hope you continue to improve it (unlike me with the project I've been working on for a year).