Doubling as a funny moment is the scene just before the Bahamut Fury fight. Genesis summons Bahamut Fury, Zack gets ready to fight and... his cellphone rings, Aerith is calling him. Zack nonchalantly tells her he'll call her back because "I've got some company." as Bahamut Fury descends in front of him roaring.
Her response: "Don't keep your guest waiting."
How about Bahamut Fury's special attack? The other summons get their own impressive animations, but this one sends the dragon into outer space! Then it turns to face the moon, and shoots out it's spikes to form an energy ring in front of it. Then Bahamut reflects a FRIGGEN LAZER off the moon, and fries half a continent. By the time you realize what's going on, you're probably crapping yourself.
The beginning of the game where Zack calmly whips out his cellphone and has a conversation with Angeal while getting fired at by enemy troops. Later you find out it was a holographic simulation, but at the time it is awesome.
The beginning scene that leads up to this is awesome too. Zack jumps out of a helicopter, runs along a moving train, deflects multiple bullets, then jumps over a stream of bullets and a squad of soldiers and detaches the front train car from the others. Too bad it wasn't real.
In Sephiroth's flashback, the fight sequence between Genesis, himself, and Angeal. Sephiroth would have won if the fight had continued, but Genesis gave a decent showing with his magic advantage before Angeal stopped him. Sephiroth then starts slicing up the Mako Cannon like a carrot as he counterattacks.
Sephiroth finally has enough of Genesis' bullshit, telling him he will rot after the latter reveals the truth of Sephiroth's existence in the cruelest possible way (before having the gall to spout Loveless at him). Sephiroth's Death Glare speaks volumes.
The way the Nibelheim incident is told in Crisis Core. Mostly due to the extremely badass showdown Zack and Sephiroth had. In the original game, we just saw Zack being thrown out of the reactor core. In Crisis Core, it turned out the two had an epic sword fight. It could be considered to be the greatest boss battle in the game, if just for the fact that, much like Kingdom Hearts, the player goes one-on-one with Sephiroth.
Later on, even the arrogant and immoral Hojo himself admits he is surprised by how much strength Sephiroth was using in order to beat Zack. Not only does he believe that Sephiroth must have acknowledged Zack as a true SOLDIER, but he even goes as far as to wonder if Sephiroth was actually going all-out against him. This only makes how serious Sephiroth's expression was when he was fighting Zack more noticeable. He definitely wasn't playing around with him like he toyed with Cloud during their fight on Advent Children. This also goes to remind us where Cloud's path to becoming some of the greatest warriors on the planet started. It was due to Zack's memories that gave him the abilities to go as far as he did without having his own skills. And even after Cloud gains his original skills, it's clear that Zack is still the better warrior and stronger fighter.
Following up Zack losing against Sephiroth, we get a recreation of the scene where Cloud stepped up, with the much greater graphics of Crisis Core. Cloud runs Sephiroth through with the Buster Sword, which Sephiroth survives. As he's trying to walk away, Cloud attempts to stop him again, just for Sephiroth to swat him aside despite his injuries. But as he impales the fallen Cloud, Cloud grabs the Masamune, pulls himself deeper onto to it, and use Sephiroth's own sword as leverage to lift him off the ground before tossing him into the Mako. Sephiroth can't believe what he's seeing, after beating the other top-ranked member of SOLDIER, he was stopped by a lowly security grunt. Though in fairness for both Sephiroth and Zack, it was probably Zack's efforts that weakened and worn down Sephiroth enough for Cloud to finish him off.
One of Zack's Moments of Awesome was charging at the entire damn Shinra Army, knowing he's going to die, then proceeding to defeat most of it and despite laying in a pool of his own blood and being full of bullet holes, he still manages to say good bye to Cloud.
This is also a Moment of Awesome for Square Enix's storytelling abilities. Players know what's going to happen, and are probably expecting it to be in a cutscene. "ACTIVATING COMBAT MODE." "Wait, what?!!" Cue an incredible Tear Jerker as you proceed to play through Zack's last stand, set to heartbreaking music, and finally revealing the reason behind the silly luck-based DMW system: allowing the game to flash Zack's life before your eyes right on your PSP screen as he's slowly worn down and his mind starts to shut down. It doesn't matter how many soldiers you kill, they'll overwhelm you eventually. Then comes the final part of the battle, with a bloodied Zack barely able to move and lift his sword, struggling to take down the last few troops, and the reels are glitched up and stalling as he desperately clings to the last memory left — Aerith. Just as the final bullet hits Zack in the rain, Aerith's portraits finally line upbefore the DMW crashes for good. It's an amazing example of Gameplay and Story Integration.