Thanks for your feedback!
I've been working on enemy layouts and improving the visual coherence a bit. Also new throwing mechanics highlight the strength of throwing enemies (even over using the pick-up guns) but I do need to redo the tutorial to highlight that more. So that's my plan over the next weeks to improve those things.
As far as the shader is concerned, I ended up trying a lot of different things for this. Trails within a single shader itself ended up being kind of tough because of all the draw calls it ended up dragging on the GPU pretty hard. My current method uses sprite trails, and I also have a ribbon mesh renderer method I use sometimes. Both are actually pretty performant but require to write the code around performance. Happy to see what I can dig up if you are interested, or just want to chat about it on discord or something. LMK.