The relationship that Sarah has with the good T-800/Pops. She does see him almost exactly like a father figure.
Seems to go both ways. Pops kept her drawings and photos at the hideout during the 30 years he was waiting for her and Kyle.
Also, right after Kyle and Sarah jump forward 33 years into the future, the Guardian looks almost sad.
Once Kyle sees Pops's damaged right hand tremble and seize up while they were loading bullets into mags, he tries to reassure the T-800 with his own iconic line when Pops just says that he was old.
Kyle Reese: *In reply to Pops* But not obsolete. Pops: Not yet.
When faced with Sarah being held hostage by John Connor to stop his opponents triggering their bombs, even when Sarah orders Pops to detonate it, the Terminator replies "I cannot kill Sarah Connor" in a manner that demonstrates it is motivated by emotional factors rather than just adhering to its programmed duty to protect her.
Being raised by Pops also effectively spared her the horrors that she would've experienced in the previous timelines including being branded as crazy, locked up in a mental hospital and abused by its staff. Not to mention all the times she "shacked up" with anyone who had the knowledge and skills she wanted her son to learn.
Another thing to consider is that everyone who died in 1984 and 1995 are alive and well. The police station massacre never took place, Matt and Ginger don't die, the gun store owner doesn't get killed, and so on.
Near the end, right before his attempted Heroic Sacrifice, Pops tells Kyle to "Protect my Sarah".
After Pops seemingly dies, Kyle tells Sarah: "He loved you."
The fact that Kyle Reese and Sarah Connor finally has a chance to fight side-by-side is heartwarming in itself as it is awesome. Along with the help of the reprogrammed T-800, and we get three of the franchise's most iconic characters fighting together. It's a real shame that John Connor made a Face–Heel Turn, otherwise we'd get a full set of Badass Family.
The ending. It's probably the most upbeat and lighthearted ending in the whole series (discounting the T2's alternate ending). Judgment Day has been prevented (for now) and Genisys is (mostly) destroyed. Both T-800 and Kyle Reese live to see another day, having avoid their own tragic deaths in the original timeline while T-800 also gets upgraded with the T-1000's abilities to boot, and Sarah Connor can finally choose her own path to live her life as per her motto "No fate, but what we make."
When John Connor explains that Skynet has sent the first Terminator back in time to eliminate him, Reese is not the only soldier to immediately volunteer to make the risky, borderline kamikaze, one-way mission to stop the assassin.
When the aged O'Brien reveals that he never forgot Sarah and Kyle saving his life back in 1984, and helps them escape from the T-3000 out of gratitude.
When Pops is in the time vortex, willingly sacrificing himself to destroy the T-3000 and save Sarah, there is a brief moment where he looks like a tear is forming in his remaining eye. One is reminded of the line from the end of Terminator 2: "I now know why you cry, but it is something I cannot do." It took decades, but it appears that this T-800 learned how to do exactly that.
John Connor, post Face–Heel Turn, still gets one when he promises to protect the still-vulnerable Skynet/Genisys AI. He may be hijacked by Future-Skynet, he siding with an artificial intelligence slated to attempt to wipe out humanity, but he also clearly cares for it.
John meeting his parents in 2017. For Kyle, it's a reunion between brothers-in-arms, and for Sarah, she's meeting her adult son that she hasn't had yet ("Hi, mom."). Later in the parking garage, Kyle is also delightfully shocked to learn that John is his and Sarah's son.
Although John has been assimilated into a terminator at this point, it almost sounds as if there's still a remnant of his human personality when he reveals to the truth to Kyle, as he sounds positively elated that after years he can finally share this information with him.
