Thanks for playing! Great to hear that this as a base seems solid to continue on, was what I was mostly hoping for. Am personally quite found of mixing styles and will most likely experiment even more with 3d/2d stuff later on.
I do agree that there are some very big balancing issues at play, the shooting enemies take something like 15 hits, don't know why I thought that was a good idea :P but that stuff comes with testing. Nice that you noticed the shielding! Might have to add a bit of a hint of how it works, but wanted a system that not just "health" and think this regenerative "health" works well in a space-shooter setting, and as you say, changes the way you play depending on the shield status (able to take more/less risks).
A had a very long wish-list of stuff I planned for, spent way to much time thinking up stuff. So power-ups etc are very much in the works :) Was even thinking of having direction ship-upgrades (that changes the ship), in-between missions etc. but we will see. Love the idea with branching paths, now that you brought it up I think I have seen it before in other top-down-shooters, will look-up some examples of this. Would differently add both more repeatability and make the levels themselves more interesting.
Also, great score! The Super End was really there, as you mentioned, for me to have a somewhat of true "ending" to the whole thing :P So added extra spawners that made it basically impossible to continue for long after a while.
Thanks for your thoughtful comments! Hope to update this in the coming weeks.