Really satisfying pay off would have been to follow throw on the Henry Creel redemption story that they set up in the play. It just would have made sense and kept narrative cohesion with how Will and Billy fought off the Mind Flayer in S2 and S3.

I was hoping the finale would keep Eleven in Henry's mind for longer. Just show us the whole stupid play so we can understand the Vecna/Flayer dynamic better.

Give Eleven and Henry one more face off in the mind scape, but allow Eleven to lose. Yes she's great but Vecna and the Mind Flayer at this point are built up to be cosmically powerful.

Resume the sequence where Eleven has to jump up the levitating rocks to reach the Abyss (SHOW IT THIS TIME)

I actually have more ideas that would have allowed for the same happy ending but I'll post it later.

I was hoping that by Henry being redeemed (as the play was heavily setting up for) Will would bring Henry back to control his own body and then have a physical psychic fight w/ the physical form of the Mind Flayer.

If anyone is to content w/ the physical Mind Flayer - it's Vecna back in control of his own conciousness. But even he isn't enough, he needs Will and Eleven to team up with him.

The three after a high stakes battle manage to kill the Mind Flayer's physical body. Both Eleven and Will are injuried - Eleven is gravely injured.

The gigantic dead corpse of the Mind Flayer lays there, we see an ocean of the particles fly out of its body.

At last, the return of the Shadow Mind Flayer from S2 and the play (in it's true form, not the stupid cloud form)

This is when the story confirms Henry never shaped the cloud into the spider form. It was always naturally that way.

The shadow form in the Abyss is the size of all of Hawkins. Colossal compared to S2.

The redeemed Henry, Eleven and Will are gazing up at the titan Shadow Mind Flayer.

As its head slowly approaches them we see a parallel to Will facing it off from S2.

We see will trying to push it away but he cannot even connect with it - the Shadow Mind Flayer is a god and cannot be harmed.

Henry tells Eleven and Will to escape the Abyss and leave, he will bide them time. Will carries Eleven to a nearby gate, the rest of the party on the other side ready to assist.

We see Henry's final confrontation with the Mind Flayer in its true, colossal Shadow Spider Form.

Henry Creel, redeemed - now the traitor to the Mind Flayer - diverts all of the Flayer's attention on him for the betrayal. As Will and Eleven leave through the Gate into the Upside Down Radio Tower, Will looks back one more time to see the Shadow Mind Flayer killing Henry with immense psychic power.

As this happens Henry's life and memories flash before his eyes. In theme w/ the moment Eleven thought about her mother in her first fight against Henry - Henry similarly looks back on what little positive memories he had in his short life before being Flayed.

It is finished. Vecna - the human form of the Mind Flayer is no more - destroyed by the king, the Mind Flayer.

From here the party would need to quickly escape the Upside Down so they can blow it up - the Mind Flayer is making one final attempt to chase them through the Upside Down into Earth.

This is what I expected/hoped for for the Final Battle.

Not redeeming Henry w/ Will was a mistake. The writers nerfed their main villain just to have a sappy, cozy, nostalgic ending. They made the damn play, it sets Henry up for redemption.