Blink's use of portals is absolutely mind blowing, especially when used by Colossus to gather inertia and take out several Sentinels.
As well as Blink's own last stand against the Sentinels, making them hit each other, until three stab her from behind.
Quicksilver's Bullet Time run through the Pentagon kitchen, stopping the guards' bullets from hitting Logan, Erik, and Charles, and also managing to get the guards to hurt themselves.
All while listening to "Time in a Bottle" by Jim Croce, which is fitting.
Even prior to that scene, when Quicksilver and Magneto blur past security making them slowly levitate in the air for a couple of seconds in Bullet Time before hitting the ground.
Magneto is likely at or around the peak of his mutant power in this film, and it shows. Among other things, he levitates the entirety of RFK Stadium, takes it with him four miles across town in mid-air, drops it around the White House, whilst controlling multiple Sentinels. And he doesn't even seem to be straining himself. And let's not forget his contribution to the final battle in the future prior to getting wounded. He hurls the X-Men's jet into the throng of the Sentinel ships and uses Bishop and Storm's powers to detonate it, taking out what seems to be a good chunk of the Sentinel forces and buying Logan extra time.
Mystique, Havok, Toad, Ink, and Spyke taking down a group of Trask mercenaries effortlessly.
Pretty much every scene with Sunspot. While he isn't in the film for long, he steals his scenes. Especially when we first see his powers, that little yelp when he lets out and lights up (with his creepy eyes even) and then suddenly unleashes his sun powers on the Sentinel. Oh, and before he dies at the end, he loses an arm, but KEEPS FIGHTING until the bitter end.
Can we also mention the fact that Erik is in his eighties or nineties at this point?
The explosion is so bright that, for a few seconds, it literally looks like day. A crowning moment both in-universe and out.
Just seeing Magneto fight alongside Xavier and his X-Men is an amazing and heartwarming sight for both casual and longtime fans. Despite him and Charles being Friendly Enemies for so long, their combined powers showcase just how well they complement each other, especially with the X-Men and other mutants fighting at their sides. If they were up against anything but the Sentinels, it's easy to picture them being almost unstoppable on the battlefield.
The fact that, when the China team announces that the Sentinels have found them, Erik just gives Xavier this brief "I got this" look and steps outside to assist in the defense.
Iceman finally showing us how badass his powers can really be, by fighting a Sentinel while simultaneously ice-skating in his ice-form.
Magneto ripping the entire safehouse out of the White House.
Hank/Beast beating the crap out of Erik/Magneto when the latter attempts to murder Raven/Mystique.
Wolverine easily brings down three Mafia goons after calmly warning them that they have no chance against him.
And then effortlessly tanking their subsequent gunfire and treating it as a petty annoyance. The goons' Oh Crap expressions are priceless.
The Stinger: We see a huge crowd of Ancient Egyptians chanting "EN SABAH NUR" in unison, before the camera reveals the very same mutant (Apocalypse) effortlessly assembling an entire pyramid with his mind, with four people on horseback atop a dune in the background. Needless to say, the next film is going to be... epic.
The younger and older versions of Charles Xavier telepathically conversing with each other... THROUGH TIME. It's a rather profound and potent moment of past and future colliding.
Charles taking control of Erik and using his powers. It truly illustrates just how powerful Charles' telepathic abilities are and shows that even Erik (who is likely at the peak of his power in this film) can't stand against Charles without the helmet to guard his mind. And considering how the rest of the film went, it's really awesome to see Charles reclaim and wield his powers without fear or extreme pain.
Speaking of pain, the scene is made a little bit more awesome by the fact that he had spent the last few minutes pinned down by debris from the stadium, visibly bleeding, and it wouldn't be surprising if he had a few broken bones. And none of that seems to affect his concentration.
Charles refusing to take the serum and getting back into his wheelchair after a decade-long Heroic BSOD (partially caused by his disability and his powers) is a MOA for inner strength. Sure, it's temporary, but that's part of what makes it awesome: even in the midst of a BSOD, he will at least try to do the right thing.
Raven tracking down Erik after what's at most a day. In a foreign city. Without telepathy. She then isolates him, threatens to shank him if any metal so much as twitches, gives a short "The Reason You Suck" Speech, and off she goes to vanish into the crowd. It's clear she'll be no pushover in this film.
In a quiet moment after everything that happened in Paris, Magneto is studying the film which contains blueprints of the Sentinels. He uses his powers to (a) hold the film reel up in the air in front of a light, (b) hold a lens in front of the projection, and (c) control a needle suturing closed a wound in the back of his head that he got from Beast pounding him into the fountain. Being able to do so many precise movements at the same time is in its own way just as impressive as throwing around hundreds of tons of metal.
Meta-Example: Days of Future Past managed to repair the disastrous continuity errors within the X-Men Movie-verse. As of this film, there have been 7 films in the saga:
X-Men appears to be in continuity with Future Past, as Future!Charles tells Logan how he helped Logan regain his lost memories, which occurred at the conclusion of the first film.
X2: X-Men United is most definitely in continuity, as it shows scenes from the Weapon X experiments at Alkali Lake.
Origins is in continuity due to a flashback of Victor Creed stepping on Logan's bone claws. The Weapon X footage is from X2, however, not from Origins.
X-Men: First Class and The Wolverine are also in continuity, as they lead directly into Future Past; the former being the prequel to it, the latter leading directly into the future scenes.
It also wipes out all these continuities at the climax of the film, so this is really a moot point now. The original trilogy at least.
The Sentinels are indeed perfected Mutant killers who take out people who are clearly experienced with their powers and fighting in general. The list includes having enough raw strength to rip Colossus in two, being able to adapt to any superpower, ice to counter fire and fire to counter ice, and understanding powers quickly. They manage to stab Blink twice.
Hearing James McAvoy's Xavier perform the voiceover for the first time in the franchise is quite exhilarating because you can sense that he is gradually becoming Patrick Stewart's Professor X.
1973 Charles: The past: a new and uncertain world, a world of endless possibilities and infinite outcomes. Countless choices define our fate; each choice, each moment, a ripple in the river of time. Enough ripples, and you change the tide, for the future is never truly set.
Heck, just listening to Patrick Stewart narrate The Teaser for the first time in 11 years is wonderful in itself despite the bleak subject matter.
2023 Professor X: The future: a dark, desolate world, a world of war, suffering, loss on both sides. Mutants, and the humans who dared to help them, fighting an enemy we cannot defeat. Are we destined down this path, destined to destroy ourselves like so many species before us? Or can we evolve fast enough to change ourselves, change our fate? Is the future truly set?
Just seeing the beloved casts of characters from both the X-Men Trilogy and First Classworking together in the same movie is awesome in itself.
It's very subtle, but Patrick Stewart's performance in the Alternate Timeline is different from his previous scenes and the rest of the franchise. He is essentially playing an elderly version of James McAvoy's character, capturing a small part of the latter's bubbly exuberance. (Charles is in his late eighties/early nineties in 2023, so his energy level is obviously a lot lower than that of his 1962 self.) Stewart's Professor X has traditionally been more serious and guarded, but the one Wolverine speaks to near the end of the movie is more light-hearted and open. Stewart has stated in an interview not long after X-Men: First Class was released that he had enjoyed McAvoy's portrayal of the young Xavier, and wished that he could emulate some of it should he ever have the chance to play the character again. Well, the actor did exactly that!