Great job! I've always been a sucker for games with this type of aesthetic. I like how dynamic it looks with the multiple scrolling layers.
It can get a little busy, making it difficult to see where enemies are. But I think that's mostly due to the explosions in the background layer that are the same or similar colors to the enemies. Maybe if you kept the explosions in the background to a contrasting color (Like the blue you're already using for the buildings, which contrasts great), it'd be easier to keep everything separated.
Overall though, it looks great! Good job!