This is truly excellent. I've been playing the last couple of hours and it's a blast. I've got one bug report and one feature disparity with the arcade to report:
1) Achieving a high score simply replaces an entry on the high score table and doesn't push the other entries down the board.
2) Enemy selection is not as it is on the original where it's largely fixed. When the robots hit the bottom of the screen on this version, the enemy they transform into is always random, whereas it varied by level on the original. This is most noticeable on Level 5, where the arcade exclusively featured the "bouncing ball" style enemies.