It's a pretty good start, but not without its flaws.
1. The scanline effect is a bit much. Make the dark lines a bit more transparent.
2. Holding space should keep firing as long as there's energy.
3. The first enemies are too fast, and shots move too fast. It's not like a bullet-hell, but trying to react quickly.
4. Bullet-hells generally involve more bullets. But ones that move slowly.
It looks good, and the controls are fine.