This is really great feedback and much appreciated! Near the end I bounced back and forth on what to give the player to start and I think it ended up being not quite right -- the ability to defend yourself seems like a minimum even if it's not powerful.
The intention was for the gameplay to be a progression from weak prey to an unstoppable powerhouse, so you aren't far off the mark with your assessment but ultimately the pacing was probably just too slow. :D
I encountered the same bug you did with the mouse control in windowed mode specifically which is a mystery to me, but perhaps the HTML version requires a cursor position reset when entering mouse capture mode. Perhaps next time I can avoid making players dizzy.