Watching Frank and Julia dance to Elvis music in 1969. It's so adorable that even six year old John and Gordo smile.
All the people in the neighborhood gathering at the Sullivans to watch a baseball game, as "Take me Out to the Ball Game" plays in the background.
It gets a call back in the epilogue of the movie, where the present day neighborhood all plays a baseball game, and Frank proudly embracing John and John's own kids is intercut with a montage of new happier memories of John growing up with both of his parents.
The look of relief on John's face when going over the Nightingale case files, he realizes that Carrie Reynolds file has vanished. Meaning his father was able to save her, proving they could stop the Nightingale killer.
John getting to talk with the 1969 version of his mother on the radio.
That and John's smile when he says hello to his six year old self.
As soon as John gets home after the timeline's changed (now Frank and the homeless woman survive the fire) he finds the message his father was writing for him: "I'm still here, Chief".
Then John and Frank start to talk, first about what just happened, then they go on to random topics like baseball all night long.
When a present day, elderly Frank is revealed to be alive and saves John from the Nightingale Killer, and says with his voice cracking "I'm still here, Little Chief" and embraces his son.
Having grown up all her life thinking her father was a dirty cop, Raimy is now hit with memories of this new timeline where her father lived to help her grow up and give advice.
The best moment is Raimy showing up at the station for her first day in uniform and Frank there leading the cops applauding her.
Given how Frank spent twenty years condemned as a dirty cop in the old timeline, seeing him welcomed with applause by his co-workers when he survives in the new 1996 is moving.
Raimy and Frank are able to stop a man from killing a woman he kidnapped, and while the lack of other changes reveals that he wasn't the Nightingale Killer, Raimy consoles herself by looking up the former victim, discovering that she now has a husband and son and just posted a video of them all happily vacationing in Hawaii.
Frank's reaction after hearing that in the restored 2016, Raimy is engaged, Julie made the leap from Nurse to Doctor, and his daughter is finally happy once again.
The online epilogue released after the series was canceled recreates the film's Earn Your Happy Ending. Frank fixes the radio and talks to Raimy one last time; we learn that the Nightingale Killer was caught after all and recently died in prison and that Raimy is planning her wedding to Daniel, with her mother going a bit nuts over it. She begs Frank to prevent his death in 2011 just before the radio cuts out, then turns around to see him standing right behind her, alive and well, and the two tearfully embrace as she gets flashes of her new happy memories.