But I'm gonna say it's my favorite season.
They present the idea of growing up and losing your childhood innocence very well. If you think about it, Eleven has been fighting back sex monsters that she created (she's the only girl in a group of kids originally and there have been a flower-shaped demigorgorn and the season 3 monster that chose a very sexual character for its host). Twist is that this time around, the sex monsters infected her and she lost her magic (her childhood innocence). She also lost her only father figure basically because that's the course of life, right? You lose your childhood innocence, become capable of reproduction and when you leave kids behind you have fulfilled your duty and can now die. I guess the irony here is that the theme of Stranger things is not a strange one at all.
Will is going through a similar transition into adulthood, so I am really curious to see what's in store for season 4. I think the only way for the magic to come back would be by being around those who are still innocent (ie an even younger character)