An intense moment that I could think of on top of my mind right now is the World War III event where Black Adam goes on a rampage against all superheroes across the world. That's a pretty powerful moment for sure. I get what your trying to say, I'll try think of more moments that I find "intense".
I think my favourite one is in Superman grounded part four. I haven't got the scans but superman is walking through Illinois. It Starts out with a young boy wanting to meet superman and it's revealed that his father beats both him and his mother. In part four superman is haunted by a dream that leaves physical marks on him and in a ingenious way lois applies make up to his face to hide the marks. Anyway the boy hears his dad beating his mom and tries to stop it but his father throws him into a basement. At that point he calls out for superman who appears and walks down to the basement to see whats happened. The boy notices the mark on supermans face and simply says "Does your dad beat you as well". The dad notices the basemnt door is open and suddenly screams for superman to get out of the face who takes him to prison. But the special part is at the end when superman gives the boy a card with his number on and tells him to ring everyday and leave a message no matter how long. If ever he doesn't call superman will return to see whats up.
TL;DR : Superman grounded shows why superman will always remain the best hero in my eyes.
Wow, I'm amazed I found this with a simple google search, but then again I'm not. It was a New Mutants issue about a young artist who was a mutant and sculpted light.
synopsis from wikipedia:
While a dance was held at his school, Salem Center High, Larry Bodine stood outside, too nervous to enter. Looking up, he saw Danielle Moonstar, who had been at the dance with the rest of the New Mutants, fly into the air on her winged horse. Larry instantly created a light sculpture of her, but when he heard voices, immediately destroyed it. Ms. Hogarth, Larry's principle, introduced him to Michael Xavier (actually Magneto who was acting as the headmaster of Xavier's School at the time). Ms. Hogarth encouraged Larry to go inside and try to make some friends, and suggested he dance with Kitty Pryde, who just wanted to go home. Despite that, Kitty latched onto Larry, and he offered to get her some punch.
At the punch bowl, he overheard some of the other kids from his school making fun of mutants, and when they claimed he was ugly enough to be one, Larry firmly denied it. As he returned to Kitty, his schoolmates decided to play a prank, leaving a note claiming they had called X-Factor on him. Larry had no time to react to the note, as Kitty asked him to head to Harry's Hideaway with her and the rest of the New Mutants. Kitty and Larry continued to dance at the Hideaway, but Larry was a ball of nerves, worrying that maybe Kitty and her friends hated mutants, like the kids at his school. Trying to break the ice, Larry told some anti-mutant jokes, which just managed to anger Kitty and her friends, who ditched him.
Back at his house, Larry continued to freak out, worrying about X-Factor. He began to call his parents, who were on vacation, but hung up before the call was placed. Finding no solace in alcohol, Larry went up to his room, where he considered calling Kitty and apologizing. But before he could talk himself out of it, the phone rang, and the voice on the other line told him that X-Factor were coming for him. Too scared to face what they might do to him, Larry committed suicide, hanging himself.
It was such a punch in the gut to me back then, and to this day I still think of that kid... just being an artist, making beautiful things- and such profound fear of being found out driving him to end his own life. Too many parallels to my own life I guess ( artist, transgendered, closeted ) no wonder it hit home.
Ultimate Spider-Man is basically responsible for my love of comics, so I actually could not read Peter's death for a while. When I finally read through it, it was handled so well and just served as such a perfect closer to the 10+ years I had invested in the series. And now, I love Miles Morales!
Lets see, some other examples...
Dr. Manhattan's reflections on Mars, so cold but so insightful and tragic.
Brightest Day had a ton of emotional moments between Hawkman and Hawkgirl being cursed to be apart.
Can't find scans but in Ultimates issue 3 ("21st Century Boy") Cap goes and meets Bucky as an old man, and finds Bucky married his old lover who can't bear to see him. I always remember that as being a powerful moment.
But these are all sad. There are too many other moments to list!
When Bruce realizes the new red hood is actually Jason Todd or when Xorn reveals himself to actually be Magneto the whole time or when Colosuss sacrificed himself for the legacy virus an the classic death of ultimate spiderman............. then in the movie XMEN Last Stand after professor X dies pyro says something bad about him an Magneto turns around to him angry an says "Charles Xavier has done more for mutants than any of us"
I'm struggling to find scans, but one of the more powerful moments I have read is from issue 45 from Busiek's Avengers run. This it right when the Kang Dynasty is starting and Cap, Thor, and others go to contain the Presence in Russia. Cap is effected and Thor thinks he is dead. He goes berserk and goes on a tirade how Cap is best of mankind and it's a travesty that he would be taken like this. He would have completely destroyed the Presence if he did not find out there was a way to reverse the calamity.
In a similar vein. There is a very emotional scene in Mark Waid's run of Cap when everyone thinks he is dead in issue and everybody is basically saying how great he is. Hercules though, says, "On Olympus, we measure our wisdom against Athena... Speed against Hermes... Power against Zeus. But we measure courage . . . against Captain America.'