Great work!
The leaderboard is a great feature!
Some points you could look into:
- Player hitbox: I felt like losing without touching the enemy sometimes
- Not sure about the autofire. If the idea is to have this more tense/tactical game, I would rather have control over when to fire because each bullet can become a huge threat.
- Maybe add rewards/upgrades at specific milestones, like every 10 seconds? Some ideas - pulse that clears all enemies, arena size increase, one HP shield.
Overall, very cool mini-game!