I really like the Holly character. She's not a Mary Sue, she has flaws but has a gift. Her inner monologue is relatable and her thoughts, especially about her mother are layered.
This book very much shows the darker side of human nature. Selfish people disregarding the needs of others. Narcissism driving wrong headed thinking and conclusions to horrific effect.
I like seeing other familiar characters and seeing them grow and change positively.
Don't let the negative reviews dissuade you. King is no fan of Trump and hundreds of butt hurt MAGAs who clearly didn't read the book inundated the reviews.