Bob Gale: For years, Marty was told that Doc Brown was dangerous, a crackpot, a lunatic. So, being a red-blooded American teenage boy, age 13 or 14, he decided to find out just why this guy was so dangerous. Marty snuck into Docís lab, and was fascinated by all the cool stuff that was there. when Doc found him there, he was delighted to find that Marty thought he was cool and accepted him for what he was. Both of them were the black sheep in their respective environments. Doc gave Marty a part-time job to help with experiments, tend to the lab, tend to the dog, etc.
I loved the little moment just after George knocked Biff through the ringer, then kindly asks Lorraine if shes alright. It's just so cute!
George: Are you okay?
Lorraine: (silently nods)
And the way they walk off together! CUUUTE!
George and Lorraine's first kiss while "Earth Angel" plays.
Finding out that Doc really did use Marty's advice.
Marty: What about all that talk...about screwing up future events? The space-time continuum?
Doc: Well, I figured, what the hell.
Marty's time spent bonding with Past!George was surprisingly endearing.
Culminating in George's goodbye line to Marty before the latter returns to the future: "Well, Marty, I want to thank you for all your good advice. I'll never forget it." And he doesn't.
When the Libyans arrive the first thing Doc says is "Run for it Marty!!" and it's emphasized even further by the Last Words he says: "I'll draw their fire!" This shows even the easily frightened Doc cares more about his friends than he does about himself.
It's pretty heartwaming to see the Hidden Depths of future mayor Goldie Wilson. In 1985 he's been described as a bad guy simply because he wanted to replace the clock tower despite it being a major part of history. However in 1955 Marty himself sees that he was simply a good guy trying to make a difference. He even tries to advise George McFly to stick up to Biff during his first appearance. Despite not liking his job triumphantly marches with his mop in hand saying the following:
Goldie Wilson: Mayor Goldie Wilson, I like the sound of that.
Jennifer writing "I love you!" next to her grandma's phone number for Marty.
1955!Doc's triumphant yell when he sees the Delorean go back to the future. Part of that was definitely it finally sinking in that he finally made something that worked.
I always loved the fact that what started everything in the second movie was the fact that Doc wanted to save his friend's (Marty) future family. I found that rather endearing.
My personal favorite from this movie was something I didn't even notice the first time through. When Marty talks to Old Biff in the Cafe 80's and Biff makes fun of "Marty Jr." for having a complete loser as a father, Marty reflexively insists George McFly is no loser (as he very well knew after the first movie). Biff's immediate response is: "I'm not talking about George McFly!" He could have made fun of George as well (as in "Well, yeah, him too, but I meant Marty Senior") if he'd wanted to, and it's glossed over with all the rest of the future antics, but I thought it was really sweet that deep down, cranky Old Biff truly respected George McFly.
Doc's reaction to seeing Marty in 1885.
Doc: Marty, I gave you explicit instructions not to come here but to go directly back to 1985.
Marty: I know, Doc. But I had to come.
Doc: But it's good to see ya, Marty.
And then they share a bro hug!
Emmett and Clara at the telescope.
Clara: I think the lens may be out of alignment, because if you move it this way, the image turns fuzzy, see? (moves closer to Emmett) But if you turn it ... the other way...
Doc:(gazing at Clara) ...everything becomes - clear.
The final scene of the trilogy, in which Doc and his clan travel from the 1890s to the 1980s to visit Marty and Jennifer. Highlights include Doc giving Marty the photo of themselves with the clock, and of course:
Jennifer: Dr. Brown, I brought this note back from the future, and now it's erased.
Doc: Of course it's erased.
Jennifer: But what does it mean?
Doc: It means, your future hasn't been written yet. No one's has. Your future is whatever you make it. So, make it a good one, both of you.
Marty: We will, Doc.
On the train, Clara just happens to be sitting in front of the salesman Doc was speaking with at the bar, who's recalling Doc's conversation with him about her, and she overhears her name.
Clara: Excuse me.
Clara: But was this man tall, with great big brown puppy dog eyes and long silvery flowing hair?
Salesman: (surprised) You know him?
Clara: (sighing) Emmett!
The fact that she can recall such details really shows how much they loved each other.
The scene where Marty goes to get his truck, Biff comes out of nowhere not knowing it's Marty (He was wearing his Eastwood Outfit.) at first because he thought someone was gonna steal Marty's truck. He of course reverts back to his "Nice Biff." persona when he is mistaken, but the gesture itself is pretty heartwarming.
Marty finally being reunited with Jennifer near the end of the movie, after worrying about leaving her in 1985-A in Part II. The way he gently wakes her up, and her relief when she says "Marty!" as they hug (considering that the last time she saw him, he was an older, broken man who had completely changed from the boyfriend she knew) is really sweet.
Not to mention that they actually got their kiss without interruption. For once.
Jennifer seeing the "You're Fired" notice disappear and Doc telling her that the future she saw where Marty is a bitter old man no longer exists and They are both free to choice Their own paths:
Doc: Your future hasn't been written yet. No one's has. Your future is whatever You make it. So make it a good one
Also when Marty and Doc first re-unite after months
Marty: Doc, we've only been back together five minutes and we're talking about the end of the universe. I missed that.
In Episode 3: After suffering an emotional breakdown, Citizen Brown sees the design for the flux capacitor in Doc's notebook...and begins to recover his true self. His whisper of "Great Scott!" as he realizes the truth that's been nagging at him all these years — and his subsequent enthusiasm and joy as he races off to get started on fixing the time machine — is simply beautiful.
Also from Episode 3: Marty's father deciding to help you. Most of the episode he's shown as a coward and a voyeur, filming people in Hill Valley without their knowing in order to get brownie points from the Brown administration. Later, when his tapes are stolen, he still refuses to help until you remind him of his father. Eight words: "Never be afraid to do the right thing."
Episode 4 has Citizen Brown taking pity on his wife-to-be despite Marty's plan to break them up. Slightly dulled by Edna's role as the Big Bad up until then, but only slightly.
Doubling as an Awesome Moment, Marty's dad punches out police to save his wife.
Episode 5: Edna finds true love with Kid Tannen, and even becomes Einstein's dog walker. D'awwwwwwwww.
Even better, in the original timeline Kid was given a life sentence in prison. Here, he's managed to turn a new leaf, now living a normal life with Edna.
Another gems from Episode 5, include Young!Doc and his father making up for their behavior against each other and also finding out why Doc went into the past: to give Marty a McFly lineage book, from Seamus to present.
Speaking of why Doc went to the past, it becomes sweeter ESPECIALLY when you find out why he went back to 1931. Doc had no info about Marty's grandmother Sylvia...because she was under the stage name Trixie Trotter! Thus Arthur eventually married the girl of his dreams!
After helping young Emmett to achieve his Hill Valley Expo Demonstration to give him back his dreams of becoming a scientist, Young Emmett asks for an explanation about who Marty is. Marty gives him a future newspaper piece, making him promise to never look at it until 1986 when he will be given the key of the city. After Young Emmett walks away and asks if he will see Marty someday again, Marty answers "I guarantee it.". Then Marty witness 1986!Doc coming out of the DeLorean and saying "You have a theatrical way of sending messages."
Also since Emmett reconciled with his father, instead of abandoning his old home, he maintains it as a part-time home when not time-traveling. So, instead of the home being sold by the bank, Emmett's just having a yard sale.
Er, not exactly. Doc's home in 1985 isn't his family mansion - it's his garage. (The one he flees to in the first movie after Marty first tells him he's from the future) A newspaper clip in the movies indicates the Brown manor burnt down sometime after the fifties (presumably because Doc had already spent his entire family fortune by that point and needed money to continue his research, assuming he didn't just blow the house up by accident. The Doc's a good guy at heart, but after ripping off Libyan nationals, he's probably not above a little insurance fraud...) This is why Marty had to look him up in the phone book in 1955, instead of just going right to his shack.
Marty and Doc sharing a hug after being seperated for a long period of time (to them). It doesn't seem like much till you take into account not only had Marty thought Doc was dead after fading from existence but he was trapped in the past with no DeLorean, no thanks to Edna disappearing into the past with it.