You can actually be proud :) the game is far from perfect as I said, but hey, it's a game made alone in 8 days and it's already great. Solo jams are hard. Otherwise, glad to read that you thought of UI particles, adding more juice and stuff, and you're definitely right about the fact that it should not reduce the clarity of the game, so knowing that, I'm sure you can work on something great without making it a complete visual mess :D About the UI particles, indeed it's a bit annoying to do. I've already used this package that works really well, just needs to learn it a little bit, it comes with a demo scene so it's fairly easy : mob-sakai/ParticleEffectForUGUI: Render particle effect in UnityUI(uGUI). Maskable, sortable, and no extra Camera/RenderTexture/Canvas. (github.com)
The SFX did not bother me, I was mostly focused on the music to be perfectly honest, but if I did not pay any attention to them, this may not be a bad point.
And you're welcome :) Feel free to ask me if you need any help!