Major Strickland holding off the aliens so you can escape. "I'm a Marine son, I'll walk on water if I have to. Now get off my fucking island while I draw its fire!"
"Gentlemen, this son of a bitch stands between us and the tunnel door. Let's take it down!"
Nomad using his suit's zero-gravity/underwater thrusters and a shotgun to travel through the zero-G alien ship, battling its occupants along the way, is one of the most magical (though frustrating) moments in next-gen gaming.
The highlight of that entire experience was when Nomad was in that tunnel of light that transported him at astronomical speeds to the top of that alien tomb. It looked like Nomad was transcending reality itself and meeting the blend between digital cyberspace and physical reality, it was very reminiscent of that movie Contact where light envelops the protagonist and she is transported at light speed to a planet at the center of the galaxy. It is at that moment that Nomad realizes how monstrously, astronomically advanced these aliens are compared to humanity, his sheer horror and awe at what he sees says it all.
Psycho's final fight with Colonel Lee in Warhead. He uses Lee's Nanosuit Calibrator to make Lee's suit start suffocating him, then throws him out of the VTOL and leaves him for the alien Warship.
In the sequel, Tara Strickland revealing that she's a government plant in CELL and saving you from having the Nanosuit ripped off your skin.
Made even better? Right before this happens, Prophet's personality begins reforming and yells at Alcatraz that this is no time for him to "lie down and die!"
Alcatraz assaulting the lithoship in Central Park, particularly the moment where he takes on four Ceph Guardians at once and destroys them before charging down a flaming hallway with his skin almost literally boiling away. Also a Dying Moment of Awesome according to 3.
The CELL chatter makes it clear that, as much as they hate Alcatraz, they're also scared shitless of him.
The whole sequence in and around Grand Central Station.
Prophet using the Ceph's biological plague weapon in New York to kill off all the Ceph in that area by weaponising their OWN PLAGUE against them!
Face it, Crysis 3 is chock full of Crowning moments of Awesome.
Watching CELL's hydroelectric dam explode is glorious.
The boss fight against the Ceph Mastermind in the penultimate mission, especially notable since previous Crysis games have not really had any good old-fashioned, one-on-one boss battles, as well as the seriously frigging awesome track that went with it.
The first time that Prophet interfaces with the Ceph Hive Mind and supercharges his suit. The simple image of over a dozen Ceph warriors, including several Devastators kneeling before Prophet and acknowledging him as the strongest being in their vicinity is surreal.
Prophet and Claire shut down CELL's orbital Kill Sat weapon Archangel when it was just mere seconds away from wiping New York off the face of the Earth.
The revelation that the Alpha Ceph was mind-controlling Karl Ernst Rasch and manipulating practically everyone in the game to free itself and put into motion its plan of opening an Einstein-Rosen Bridge (a.k.a. a wormhole) to call its homeworld for reinforcements. Mind you, this is no small feat, considering that the sheer act of the Alpha Ceph opening said Einstein-Rosen Bridge means it is essentially building a bridge between two galaxies.
Karl Ernst Rasch gets one when he tells Prophet, Psycho and Claire to run while facing the Alpha Ceph which is moments away from killing him.
Psycho showing up in a gunship (with an open cockpit no less!) to catch Prophet as he jumps off the CELL tower at the VERY LAST SECOND, followed by Prophet firing the gunship's weapons at the Alpha Ceph, AND THEN followed by Psycho jinking left and right in the air against Ceph aircraft and missiles deployed by the aliens.
The ending of the game, and by extension, the series:
Psycho assaulting the Alpha Ceph, which can decimate CELL aircraft like a hot knife through butter, in a gunship to buy Prophet time, right when the Alpha was about to fully assimilate Prophet's mind into the Ceph hive mind.
Prophet, seeing the Ceph coming through the wormhole while floating helplessly in space, is sure that he has failed and the world is doomed. The screen goes black, and it looks like the game is going to end on a Bolivian Army Ending... but NO! After snapping out of his Heroic BSOD, he launches himself through space using his suit's zero-gravity/underwater thrusters (which is also a Call Back to Nomad doing the same thing in the first game) and THEN uses the CELL Archangel Satellite in orbit to single-handedly stop the Ceph invasion from reaching Earth by blowing up a continent-sized ship that looks like Cthulu's twin brother.
Then Prophet survives falling through the atmosphere, a feat that has previously only been done in the FPS genre by Master Chief and Chief needed a Forerunner door to do that. Prophet falls through the atmosphere IN HIS ARMOR ALONE.