I think the particle effects were good, but you could consider changing the colors so the player can read from afar or with their peripheral vision. For example, enemy bullets could be yellow, so then yellow is the 'avoid' color. Or if we kept enemies and enemy bullets green, their death particles could be a much darker green or a grey.
It's great that you're iterating quickly to player comments, that's a good work ethic and attitude. But don't feel like you need to iterate on everything I say, especially for a Trijam (as that defeats the purpose of the jam if your iterations take you past 3 hours dev time), I was just trying to give some advice you could think about for your next game :-)
I'll give another thought: think about scaling the difficulty of your game over time, and ideally changing the player properties so there's a sense of progression, especially for a score-based game like this. You could increase the spawn rate of the enemies in accordance with the player score. And/or create milestones for the player at 100, 500, 1000 points, etc. that increases the player's fire rate or bullet size, fires multi-shots, etc. Obviously you can interject a lot more creative ideas, but simple number scaling based on other numbers (e.g., the score) is a fairly quick and easy addition you can make to a game like this that's possible to fit in a Trijam.
Regardless, great work, I hope you keep making games! Challenge yourself to make a game every weekend for a few months and see how you improve!