I think this game could be a lot better if you made the controls better.
In the original asteroids, you can aim your ship 360 degrees without moving. In this game you can aim in 4 directions without moving, and 4 more directions when you are moving. This makes aiming incredibly difficult, and since enemies are chasing you, you barely have a way to defend yourself because you cant run away from them and shoot them at the same time. Most of the game for me was running away from the enemies and trying to take pot shots at them. The actual asteroids in the game seemed to give a lot of score but they were no threat whatsoever to the player so there's not really any use in destroying them, since score is completely arbitrary.
Additionally, the art has inconsistant pixel density and the player and enemies are really small. When you beat the game, the high score only displays 2 numbers even if it's a higher value than that. Having A and B as controls right on the screen and then not using those keys in the game is incredibly confusing. You aren't sacrificing any nostalgia by just making those keys say W and E. When you hold the fire button down, everything on and off the screen that gets hit makes noise, with the asteroids being the loudest, and at the same time, there's no visual feedback for when a bullet hits an asteroid.
That's most of the things that caught my eye when I played. While it has a lot of flaws the general idea isn't that bad. If you made some changes you would have something good to work with.