Star Trek: Nemesis
I've just re-watched this after years, and I really enjoyed it. I guess after all of the insubstantiality of the Kurtzman-era Trek, my standards are lowered? Maybe it's just age, but I do think that Nemesis starts the character study that was attempted by the Picard Series. They start to pose some great questions about the self and whether it's the product of experiences, memories, actions, etc, but then the movie doesn't really go further with it. There's a similar question being asked by the film with Data and B4, whether the self is merely the quantity of memories and information or is there more to us than our experiences.
Nemesis ends with a set-up to further explore that question through a newly re-activated B4(the replica android of Data) which already is in possession of Data's memories and experiences. In the film, Data installs his wealth of experience and memory into B4's circuitry. Instead of creating an individual who could function with a sense of itself and it's own individuality, B4 remained a husk with a child-level intellect. But, Nemesis ends with Picard speaking to B4 about Data following Data's death. Picard, obviously still blaming himself for Data's death and is trying his best to move along, apparently part of that is hoping that the B4 android will somehow fill the void left by Data. As Picard speaks to B4 about Data's character, he's called away, and B4 is humming 'Blue Skies' which was sang by Data at an earlier point in the film. Which makes Picard seem hopeful and the film ends on a hopeful note.
I wanted to see Nemesis again, mostly to see where the pre-2005 Star Trek had ended canonically and to the best of my knowledge and searching, the events of this film are where they wound up before the Kelvin Universe was borne by J.J. Abrams.
I would love to see whatever might have come after Nemesis! The character of study of Picard should've been completed there in whatever that subsequent film would've been.