The C64's hardware limitations make it impossible to improve the graphics in any meaningful way. You can either have hi-res characters, meaning you can define every pixel in a 8x8 character block or 24x21 sprite, but they can only be one colour, or you can have multi-colour meaning you can only define pairs of pixels but have three colours, two of which must be shared across all chars/sprites. I chose to go for more accurate colour over sharper sprites that are all one colour.
Contrast this with the NES that can have hi-res sprites with any three colours from a palette of 54.
Unfortunately some compromises are inevitable, if it was easy it would have been done in the 80s.
Same with the sound, it's as close I can get without the benefit of dedicated sound hardware built specifically to make Galaga's sounds that the arcade has.
I see that you can 'fire' when being captured on the arcade but this doesn't really add anything to the game, the bullets just fire off in random directions and I've never seen one hit anything. Because I'm drawing player bullets with characters, changing their X position in flight would take probably a couple of days to code, for very little benefit.
A potential great post but spelling and punctuation should improve.