Mine would be A. I. I just love drama's with some mystery and sci-fi in it. And yes I cried at the end.
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Your mentioning of A. I. had caught my attention. It indeed has one of the saddest endings I've ever saw in a movie. It has existential themes, which greatly caught my attention.
Spoilers for those that had never seen A. I.: Humanity has become extinct due to climate change/global warming and the "Mechas" they previously successfully developed had evolved and survived and they are still trying to figure out purpose, and the meaning of existence. They eventually find David and revived him as he and his Teddy Bear companion were the only 2 Mechas left that "knew" living humans. Because the Mechas believed that if they could study humans, it would be the key to understanding the meaning of existence.
Either way the point is that the evolved AIs or Mechas were able to restore and clone David's "mother" or the female human he had been attached to emotionally that way. They could only clone her to live one day and cannot repeat the process but she would spend the entire day with him. Thus granting him his wish so that his "mother" would "love" him despite that he isn't a "real" human child/boy. But David wanted to be "human" so that his mother would "love" him. It borrows some of those concepts from 'Pinocchio'.
For me it's pretty much all movies relevant in some form or way to Artificial Intelligence, Robots, Androids, Cybernetic Organisms (Cyborgs), Mechas, Automatons, Advanced Sentient Machines and so on. I find that some of them are more enjoyable and interesting than others, depending if they focused on those themes a bit more rather than splashed in.1