The sacrifice of the universe is an upsetting and cheap ending because it was also the sacrifice of everything that had been built up. Defying what was ineffable, saving the world, trying to fix the systems of Heaven and Hell and then recognising that Heaven and Hell are inherently broken.
The people they saved, the people they hurt, conversations that were never had, and conversations they otherwise should have been able to make if they had the time. The people that WE personally have attachments to, with the memories and the stories we followed.
It could have been done better. The story and the themes could have still been respected. God could have brought back the universe that was wrongfully robbed, rescinded Heaven and Hell, granted free will. Then Jesus could have guided people on what to do with that free will. Aziraphale could have helped the very street he was confronted by Sandwich for leaving to crumble. Crowley could finally live in the world he envisioned, and Aziraphale, Crowley, and all of the other angels and demons could have STILL been given lives as humans.
Everything would have been delivered to the same place, and the things that were built up, the character arcs and resolutions STILL COULD HAVE HAPPENED.