Avengers: Infinity War had made us wait for 10 years and it 18 movies to build up to this moment. Thanos was the big baddie that we all needed, and he is the best MCU villain. His character motivation is great.
The film started with one character’s death, and it had ended with many deaths. It was still full of great moments which had made love this movie.
Spoilers are ahead.
The time of grief point was when Gamora died. From the beginning, when Gamora had started explaining Thanos’s motivation, the location of Soul Stone had been teased.
Gamora’s expression at Soul Stone had given it away that she knew about this gem. She then makes Quill promise to kill her if Thanos did get hold of her. Then it had been revealed that Gamora knew where the Soul Stone was. She lied to Thanos that she never found the stone but by torturing Nebula, Thanos found a memory, and it was revealed that Gamora would never tell Thanos about it. Gamora then took her father to the stone.
At Vormir, Thanos and Gamora were greeted by Red Skull who was transferred there by the Space Stone in Captain America: The First Avenger.
He said that to acquire the Soul Stone, one had to sacrifice the soul of someone they love.
Gamora thought that Thanos never loved anyone, but he sacrificed his daughter, Gamora, the only person he actually loved. This scene was crucial to building the character of Thanos who had the intensity to love.
This is different from the comics as Adam Warlock had the stone, and because he will not show up until Guardians Vol. 3, Marvel changed things.
We never saw Thanos use the Soul Stone, but it is believed that his talk with Gamora at the end was in the Soul World.
So, if Gamora is actually alive in the Soul World, her soul could be transported out of the Soul World. This is a theory which might bring her back to life.
There is another Another theory that Gamora after the sacrifice might have been turned into the Soul Stone instead of being in the Soul World.
Thanos had given up Gamora to get the Soul Stone, but what if giving up someone to call on the power of it uses the soul of the sacrificed in order to create the stone.
Gamora might be the crucial element that the Avengers to defeat Thanos.
It is also believed that the in the Universe including the Avengers, who had been disintegrated at the end of the movie might have been transported to the Soul World as well instead of being dead.