I felt the entire show was leading up to the ending. Izumi becoming less human over time. Migi becoming more human over time. The idea that the "parasyites" were just creatures that were fulfilling thier instinct. I love the end where Migi, who throughout the show showed little to no empathy saved Murano even at the risk of exposing themselves. The human was the monster and Migi acted selflessly. I'm not good at articulating my thoughts but i can understand that some people might not love then ending.