I loved it and do not understand the negative reviews. I felt it was obvious the ending was meant to leave content for a second season, and those upset about it are used to the one season tradition by Mike Flanagan.
While it did take me an episode or two to get into it, by the end I was so hooked! The characters accurately portray teenagers, which is rare in shows these days. It does it really well, too, all things considered; there’s typical high school drama, insecurities, and relationships, but all of these are also paired with very unique and individual traits for each character. Each teenager has had to “grow up” or adjust in their own way in response to their illness and it brings maturity to some scenes and immaturity to others. It all fit where it was due.
I hope it gets renewed for season 2! I love these characters and want to see more from this universe.