The first appearance of the Executor. We see it eclipsing the light on multiple Star Destroyers! LIKE THAT BEHEMOTH FROM THE INTRO OF THE PREVIOUS FILM! Even its engine exhausts dwarf the escorting Destroyers. The same sequence debuts a new piece of music for Empire,the Imperial March.
To truly put this into perspective, normal Star Destroyers are approximately 1,600 meters long, or about 1 mile. Super Star Destroyers are 12 times longer than normal Star Destroyers. The Executor is a ship over half the length of Manhattan!
During the battle on Hoth, Luke single-handedly takes down an Imperial Walker, by himself, on foot. At that, you'll understand why the Emperor is so concerned about the kid; as in, "If the boy can do that with barely a few days instruction from Obi-Wan Kenobi, what could he do once he is properly trained?"
During the battle, the Rebels manage to disable a Star Destroyer with the Ion Cannons, creating a gap in the Imperial blockade for the Rebel ships to escape through.
After the Battle of Hoth, the Millenium Falcon is making its escape from not one, not two, but three Star Destroyers, outmaneuvering the Star Destroyers with a twisting dive. The colossal ships can't readjust their positions in time, and so we're treated to the sight of two of the three Star Destroyers nearly colliding in space. It's awesome.
Yoda: Judge me by my size, do you? Yoda: For my ally is the Force, and a powerful ally it is. Life creates it, makes it grow. Its energy surrounds us and binds us. Luminous beings are we, not this crude matter. You must feel the Force around you; here, between you, me, the tree, the rock, everywhere, yes. Even between the land and the ship. Yoda: Do, or do not. There is no "try." Yoda: "Great warrior?" Hah! Wars not make one great.
Yoda's second dialogue sounds even more awesome after you've seen what the Jedi (or any Force sensitives) are capable of in the Prequel Trilogy, the Expanded Universe, and even the Legends.
Luke informs Yoda that he's just not strong enough in the Force to raise his starfighter from the swamp. Despite Yoda's words of encouragement (see above), Luke just tells him he wants "the impossible". Yoda then raises the X-wing out of the swamp, accompanied by triumphant music and spirited beeping from R2-D2.
Luke: I don't— I don't believe it!
Yoda:That... is why you fail.
Luke Skywalker faces Darth Vader for the first time.
Vader: The Force is with you, young Skywalker, but you are not a Jedi yet.
Above all, when Luke is clinging to that ledge, thoroughly beaten by Vader both physically and emotionally. Luke defies Vader's offer - "Come with me, it is the only way." - and steps offthe ledge.. He didn't expect to survive, but it was the only course that could still win the larger battle. It was what Yoda had warned him about. Vader was not out to defeat Luke, but to corrupt him to the Dark Side of the Force; when Luke showed that he would destroy himself rather than submit to that, Vader learned that his son's integrity was too strong for him alone.
For Vader, when he starts picking up random pieces of machinery and tossing them at Luke in the middle of the fight. That's when you really understand that, yeah, Luke's pretty handy with a lightsaber, but he iswayout of his league here.
The best bit is Vader isn't even doing any psychic wavy-arms gestures, he's barely even making an effort. Imagine how brief it would have been if Vader had just wanted Luke dead.
Further emphasized that while Luke adopts the standard two-handed grip on his lightsaber at the start of the match, Vader opens with a more casual one-handed grip and bats away Luke's initial attacks with what is clearly contemptuous ease, even knocking Luke to the floor by casually pushing against Luke's most powerful blow. Those first few strikes serve as the first inkling that Luke may have just bitten off a lot more than he can chew.
After Luke scores his hit against Vader, Vader roars in rage, and viciously renews his attack, immediately stopping any pretense of Luke being his equal, and in less than three strokes, effortlessly severs Luke's hand. There's even this slight pause before he does it, as if to silently say "You are not dead, because I decided not to kill you."
The setting for this particular duel was also amazing. The eerie, low-lighting of the carbonite chamber, the fog from the machines, and Vader's breathing grimly cutting in through the silence. A truly masterful set-up to the fight.
When you think about it, Luke actually makes a decent showing, especially for his low level of training. When Vader begins the fight, he's just barely even trying. Then Luke evades his trap, and even manages to cause him some degree of pain with the coolant (if his cry of rage is any indication), and Vader resorts to throwing things at Luke using The Force. Then Luke lands a hit on Vader's shoulder, causing Vader to cry out in pain AGAIN. Only when he chops off Luke's hand is Luke finally driven to his knees. Sure, he'd probably have lost eventually anyway, but considering how far below his combat abilities are below Vader's, that's pretty impressive.
Just about everything Vader does through this fight is awesome, when you realize that he was controlling both the pace and tone of that battle the entire time. He starts off by forcing Luke to make the first overt attack (which, by the way, is in direct contradiction to the Jedi code Yoda had just taught him, making it a nice Take That! at the same time), then he almost playfully bats Luke around a little to show him what he's up against. In the second encounter, he does nothing but stand to one side and pummel Luke with Force thrown objects, showing him what a real adept is capable of, before knocking him onto the suspended walkway. And then, he goes full bore berserk on the boy, and Luke switches from mildly out-of-his-depth action hero to full on terrified and desperate to be anywhere else. And Vader lays him out in about twenty seconds. And what does he do when Luke gives him some flack after all that? He takes off his fricken sword hand at the wrist with almost no effort at all. Only then does he start delivering his true Breaking Speech. Pure badass.
Also, when Vader kills Admiral Ozzel. Ozzel isn't even in the same room, and yet he easily force chokes him through the view screen; distance is no object to Vader.note Although more to the point, distance is no object to the power of The Force. It helps that he had a very good reason for it: Ozzel's tactical blunders spoiled the Imperials' chance at a destructive sneak attack and bought the Rebels time to evacuate Hoth. "You Are in Command Now, Admiral Piett." He gives Piett his promotion before Ozzel hits the ground.
When the Millenium Falcon's hyperdrive finally works thanks to R2.
Wedge and Wes being the only Rebels to actually take down an AT-AT with their tow cables.
Boba Fett doesn't even flinch when Darth Vader gets in his face about the disintegrations.
How about the fact that Boba is able to get semi-huffy with the Sith Lord and live!
Han Solo after being tortured. When he finds out that this was all to lure Luke into a trap, he uses a bit of strength he has left to punch Lando before being restrained. Lando was in the middle of a Heel–Face Turn at the time, but the fact that Han's best friend putting his other best friend in danger being the last straw for him was pretty awesome.
As Han Solo is lowered into the carbonite freezing chamber, Leia declares her love to him. She doesn't get the response she was hoping for.
Leia: I love you!
Han: I know.
Especially since this line was an ad-lib by Harrison Ford.
"I am altering the deal. Pray I don't alter it any further."
Luke jumping out of the carbon freezing chamber right before it can freeze him.
Vader: "Impressive... most impressive."
The big reveal, is some of James Earl Jones's best vocal work.
Vader: No. I am your father.
Darth Vader just force deflecting Han's blaster shots with his hand, no lightsaber necessary, then Force-ripping his blaster across the room. You think you're going to be able to just shoot Darth Vader? Please!
Imagine yourself as Han Solo for a moment. You've just outrun a bunch of Imperials and finally made your way to a small out of the way planet for a chance to rest and repair your ship. You've met up with an old friend of yours and are on the way to a nice meal with the possibility of romancing Leia a bit afterwards. Then you open the door to find none other than Darth Vader waiting for you. Do you look in disbelief to the friend who betrayed you? Turn and hightail it out of there with Leia and Chewie in tow? No. Without a single second of hesitation you immediately pull out your gun and start shooting that motherfucker. Further proof that Han is the biggest badass to ever swagger across the galaxy; too bad Vader has more than enough power with the Dark Side to make up for that.
Then there's Chewbacca's truly epic roar. It's a real shame he didn't do that more often in the series.
John Williams' music is its usual awesomeness, but two aspects of this score particularly stand out. Firstly, the Imperial March, which makes its debut in this film; rarely has music been quite so badass. The second is at the very end of the film: The Rebel fleet has fled the galaxy after the destruction of their main base, Luke is psychologically shaken by the confrontation with Vader and learning the man is his father (not to mention getting his hand lopped off) and Han has been frozen in a block of carbonite and taken off by a notorious bounty hunter to be sold to a wicked gangster. But as Lando speeds off to rescue his friend and Luke and Leia stare out at the stars, what music is blaring behind them all? Han and Leia's Love Theme.
"Apology accepted, Captain Needa." This was also Needa'sCrowning Moment of Awesome. Having just been outmaneuvered and out-bluffed by Solo, Needa is tasked with explaining his failure to Vader, and there's no question in anyone's mind how Lord Vader deals with setbacks. What does he do? He flies himself to the Executor to stand before Vader, take full responsibility, and fall on his sword, sparing his ship and crew from the Sith Lord's wrath. Vader's quoted line seems to imply that even he was mildly impressed by Needa's actions. Compare Needa's execution to Ozzel's, whom Vader pointedly refused to acknowledge while choking him to death.
With Luke and Han both incapacitated in different ways, Leia calmly takes charge of two rescue missions, in a manner similar to her staying back at Echo Base on Hoth to direct the evacuation until the very last minute. In the previous film, Leia was the one who needed rescuing. In Empire, she's the one who rescues Luke from almost certain death, even making (with the help of Chewie) Lando back down about the craziness of flying back to Imperial-occupied Cloud City. No Damsel in Distress, our plucky Princess.
In both Star Wars timelines, the hand and lightsaber are retrieved. Let the logistics of that sink in a moment.