Thank you kindly for your detailed feedback!
Non of us knew any game with this premise so we felt pretty confident about it, but there it is!
I guess that's the curse of us game devs, nothing hasn't been done already. :D
"Though the game is endless, the difficulty never seems to increase."
Oh well we do have a difficulty curve. In the beginning there are only 2-3 enemies with 1-3 health gradually increasing to up to 10 enemies with up to 7 health at 50.000 score.
(with some enemies having 1 or 2 bonus health but are slower for slight variety)
Maybe it is not steep enough.
Anyways, thanks again for the feedback, much appreciated! :)