This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / TRON: Legacy
Seeing the once lively arcade a shuttered, dusty ruin. It hits even harder when Sam goes up to the apartment his dad used to have above the arcade floor. Those who remember the first film see the spot where the Power Trio was formed, now dark and full of nothing but dust and cobwebs, with Kevin's handheld game broken on the floor. It's like seeing The Millennium Falcon in rusting in a junkyard.
Sam and Kevin's awkward reunion can hit home for parents who are out of touch with their kids, or vice versa.
It's brief but, Kevin's understandable reaction upon realizing who it really is that's chasing them
Kevin: Tron, what have you become?
"I fight for the Users."
The flashback where Kevin Flynn sees the genocide of the ISO programs and realizes that there's nothing he could do to stop it.
Then we get another flashback the explains what happened to Tron.
In Fridge terms, the scene where Kevin reveals to his son that Quorra is the last ISO and all of Kevin's efforts to disguise her as a regular program. The scene when she tells Sam how she escaped the genocide only makes it worse.
Sam: Alan, you're acting like I'm going to find him sittin' at work, just, "Hey, kiddo, lost track of time."
Alan: (wistfully) Wouldn't that be something.
It's so sad to hear the formerly energetic and cool Kevin Flynn wearily say "Sometimes life has a way of moving you past things like wants and hopes".
Despite everything he does, Clu is a tragic character. Everything he does, it's because he was programmed to do it that way (with an astonishing lack of foresight) by a young Kevin. In the end, when Kevin confronts him, he completely breaks down because he cannot accept something he wasn't created to understand in the first place.
Alan Bradley's situation is a heartbreaker; no matter the timeline, the man can't catch much of a break. After the first film, he marries Lora, but she takes a job in DC and they're apart for most of their marriage. He's spending most of his life chasing after Flynn with a metaphorical mop and bucket, trying to run interference between his big dreamer friend and the board. Then Flynn vanishes, and he's thrust into a CEO job he never wanted, then just as unceremoniously Kicked Upstairs into a mascot position, trying to raise his friend's kid (and kid turning out to be just like his old man) while struggling to keep the ideals of his friend (Flynn) and his mentor (Walter Gibbs) alive after the men themselves are gone. And in the end, he gets a vague non-answer from Sam about what happened to his friend. One of the few dubious mercies about it all is that he apparently has no idea that Tron was a sentient being, nor anything about the horrible things that happened to his virtual son.