Retroiffic! I don't know that I've ever played the original Asteroids but this was really fun! At first I felt sort of invincible, the cubes weren't attacking me or anything so I didn't think I'd be able to die unless it was on purpose. And then I went a bit too fast and carelessly... 💥
The second time I was cautious and managed to get 40300 points by avoiding any crashes until my shards were full, which left me confused. Luckily someone else had asked about this, so knowing the trick I was able to win on my third fourth try!
The core game play is very good as it is, I'm sure people who are better at this sort of game than I am would be able to zoom around faster and safer. I did a lot of coasting and avoided the edges of the level. Even though I could tell the blue cubes were different, and rarer, I don't think I would have realized their purpose on my own.
Other than that, you could easily add any number of things to increase complexity, powerups or different targets or even static obstacles. Have you ever played Gridwars? This reminds me a lot of that, and it uses different shapes for enemy behaviours. Squares just float around like yours do, while other shapes chase or shoot bullets.