Here is what I liked about it:
Crowley got to ask his questions and Aziraphale knew he was a good angel, whether God Herself agreed or not.
Crowley asked his question, received an answer, wasn't satisfied and got to make his own choice for once. Freedom of choice was spared to him for the first time and with it he chose to free all of ours, a universe without anyone keeping score, no meddling, no punishment, no Armageddon.
Aziraphale, a being that tried to do the right thing and do right by God all his existence, had his flaws pointed out to his face. He took them without even flinching, agreed, looked Her dead in the eye, and told Her 'I'm still your second-best angel'. That moment is SO precious to me. He didn't need Her approval on it. Not only that, TO HER FACE, he proceeded to tell Her the very best angel She'd ever created was one She'd cast out.
Aziraphale told God She was wrong. He respected Crowley's final choice, whereas before he'd always get too scared to actually listen.
I liked that the ending showed the fundamental difference between Ineffable bureaucracy and Ineffable husbands. Gabriel and Beelzebub loved each other, and so did Aziraphale and Crowley. But they loved humans just as much. Humanity is a part of their story just as much as each other is. Their final act of existence was a love letter to humanity that gave them somewhere to belong.
As for the new universe, Crowley and Aziraphale getting to love each other without wounds, unspoken words, or fears that made them miserable is very dear to me.
That being said, here is what I didn't like about it:
I wish Crowley's choice had been different. Not because of the 'no us' part, but because another universe meant everyone else was forever gone too. It went against the teachings of the first two seasons. I understand why he made that choice, he was never satisfied with the initial design to begin with. He tried to desert it multiple times. But still, I liked those messages.
"You're going to burn all this away. Why? Because some adults mucked things up. That's a reason to fix it, not destroy it."
Job's children being killed and then replaced with new ones wouldn't have made the old kids less dead. Hell destroying the life on Earth was no different than Heaven destroying it.
I think I'd have preferred it if the old universe continued on without any divine involvement, in which Aziraphale and Crowley got to grow old as mortals, with memories but no powers. I wish instead of meeting each other in a universe without any baggage, they got to work through their issues together. I wish they got to learn how to communicate properly and love without fear. They deserved that much.
There! All my opinions. Lmk what you think!