I think this was a near perfect ending for the season, and an even better set up for the final season of Stranger Things. I see a lot of people complaining that they didn't kill of Max's character, but that is not the fatal flaw with this episode IMO. Because Max's story has been sending a message throughout this season, especially within Dear Billy.
It was sending the message that despite all your self-hatred, regrets, and doubts, there are still people in this world that care about you, and they can bring you out of that darkness. Yea sure, it's cheesy to say "the power of love is stronger then the power of evil," but are Vecna's lines really any less cheesy then that?
With Max's story being a metaphor for depression, I actually think that it coming back to haunt her again this episode nearly worked, but seeing so many people say they wished it killed her leaves a bad taste in my mouth. My main problem is that Vecna fully defeating Max takes away from the beauty of Dear Billy, in a way that will affect my future enjoyment of what was the best episode in the series, for me.
I understand the point of stakes and I understand people complaining that this show doesn't kill off main characters enough; while I agree with this sentiment, killing Max to open the gateway to the upside down, ultimately allowing the demons to enter and consume our world: What is that saying? If Max's story is a metaphor for depression and how your relationships with others can help you overcome it, her death should be reflective of that theme. The way they decided to write it treaded a thin line between respectful and downright awful.
Time for a weird transition!
This season set up the death of Steve's character incredibly well. It would've been perfectly in theme, in line with his long running redemption arc, and would put Nancy in a very interesting place emotionally, if he died to save her. Instead, season 4 opted to set up a love triangle between Nancy, Steve, and Johnathan for season 5. It felt like none of these season 1 characters were touchable, even in a fake out death sense. So, instead, they decided to "kill" the character whose arc has been about resisting the urge to end her life.
Technically, if this is truly what they wanted to do with her character, they could have. I don't understand what they'd be saying with it, or what themes would be displayed through that kind of writing. I just see it as hopeless. Especially when comparing it to how Eddie died this season, or how Hopper "died" in season 3. Not every death can be a hero's sacrifice death, I get that. But not every characters survival is a metaphor for overcoming self hatred.
Genuinely, the fact that Eddie's sacrifice was well written, and the fact that they gave Max a bit of hope near the end, greatly raised my ranking of this episode. Because a stories themes matter far more then it's tension. Max's character has been dealing with some very sensitive themes, so I'm moving through the rest of her character arc with caution, in season 5. But I truly hope that others can see why killing her off permanently would do damage to the message of hope this show usually seems quite committed to sending.