The battle against the Volge. From The Spirit Riders Big Damn Heroes moment, to nuking the Volge with a super bomb, and everything in between, it is straight awesome. And that's all from the first episode.
When McCawley is quite obviously about to lynch Alak, Nolan jumps into the middle of the situation, telling a lie about how he's been playing cards with the kid all night. When McCawley nods at one of his guys to get rid of this dumbass, Nolan disables him with two blows, sits right back down, and picks up the cards he absolutely hasn't been playing with.
Even better, when McCawley draws on Alak minutes later, Nolan jumps up and rips the slide off the gun in one motion.
The blooper reel shows that that wasn't fake (in the sense of CG or what not) - the slide actually gets jammed on the gun during one take.
"Down In the Ground Where the Dead Men Go"
Irisa gets herself in the middle of an angry mob while trying to rescue a Castithan from prolonged ritual torture/religious cleansing. Just as things are about to get nasty, Tommy shuts down the whole situation... by arresting the victim. For loitering.
Before this, Irisa—despite her own history with being tied up and hurt, and having been explicitly ordered to stay away from the ritual—stayed with the tortured Castithan, tried to get the children away from the ritual, and finally decided she couldn't stand by anymore, climbed the rack, and cut the Castithan down while shrieking an Irathiant war cry at anyone who tried to get near her.
"The Devil in the Dark"
Datak gets in a swordfight with two Hellbugs and wins.
Just prior to that, while Alak was understandably freaked out, Christie grabbed a torch and held it at bay until Datak took over. Pretty badass.
Datak telling off Nolan and Mayor Rosewater when they accuse him of being involved with her sister's disappearance.
Kenya having the willpower to break out of the Lotus-Eater Machine without any help, simply by recognizing a single error in the illusion.
Datak demonstrates to Nolan how knowing the people of Defiance gives him power and knowledge. Nolan then turns this around to realize that Stahma is the real brains in the Tarr family. For her own part, Stahma seems amused and flattered when Nolan gives her her due, no matter how backhanded the compliment.
Nolan's Sherlock Scan of Skevur while Datak looks more and more uncomfortable.
Nolan: "Mmm, he talks tough. You can see by his eyes, though, he's terrified. Funny thing is, he's not looking at me, Datak, he's looking at you - and I'm the guy with the gun. Mr Skevur... ooh, that cut looks nasty. I think Datak's boys got here before me, and I think they impressed on you the importance of not cooperating with me. Then I get to beat on you fruitlessly for a while until Datak swoops in, whispers in your ear and all of a sudden the information flows. I get to look like a big dumb ape, you get to look like a hero. How close am I?"
Datak: "Close enough. But for the record, I had no intention of whispering in this disgusting man's ear."
"The Serpent's Egg"
Nolan, without hesitation, passes a rifle to Amanda so she can back him up while risking his own life and giving her a chance if they flub the ruse. Rynn was so impressed that she came back to rescue him after successfully escaping.
Speaking of Amanda, Nolan's trust isn't misplaced. She blows away the hijacker's backup with a clean headshot.
Tommy, after learning what happened to Irisa and why, and after spending what looks like hours begging her to stop, finally learns that she's completely right about her prisoner's identity. She unlocks Tommy's handcuffs, and he promptly starts beating the living hell out of the bastard.
"She was a child, you piece of shtakko!"
On that note, the fact that Irisa finally stood down. The Castithan had wanted her to become an avenging angel—he wanted to torture her into a killer. She spares him so that he'll live the rest of his life knowing that he failed to turn her into a murderer.
Castithan: What are you waiting for? ...End it! No! What are you doing?
Irisa:*letting Tommy go* Ending it.
She even pulls Tommy off of him when he starts to beat him up, insisting they take him to the hospital because killing him is what he wants. Our Little Wolf is growing up.
As a result of this, an enraged Datak to demands that his son call off the wedding. Using the situation to his advantage, Rafe talks to Alak and convinces him that even without his father's support, the wedding can still go on. Later, Rafe rubs salt in the wound by pointing this out to Datak, since he now comes off as a hero to Alak and his daughter for saving their wedding. This aggravates Datak so much that he pulls out his knife, only to have Rafe pat his gun, and with the help of the mayor he calmly walks away as Datak swears to himself.
Rafe: "I have a wedding to attend."
Datak: "Oh, the wedding is off."
Rafe: "That's what Alak said. At first. Then we started talking. Your son loves my daughter, and my daughter loves him, and that's good enough for me. Oh, he may never get my mines, but I will look out for him. And I'll make sure that those kids will have a wedding that they will always remember."
Doc Yewll straight-up murdering Mayor Nicky after coming to the conclusion that, yep, she's definitely the villain. The best part? None of the other main characters ever found out that A) Nicky was murdered or B) Nicky was actually their enemy. The Doc just swooped in and settled things before anyone else realised they needed settling.
"Past Is Prologue"
Nolan one punching Datak's hulking bodyguard, and giving him a long overdue ass-beating in the streets.
And when he taunts him to finish the job? Irisa (who had to stop Nolan from likely killing him) walks back and kicks him upside the face.
Another Tarr (Alak) getting dragged aside and pummeled by Rafe and his miners, for getting involved with a prank that wound up with one of Alak's friends dead. Rafe makes it clear he's not gonna put up with anymore of his idiocy.
Rafe: "If you again act in a manner unworthy of my baby girl...your marriage will end. And I do not believe in divorce. Capice?"
"The Opposite of Hallelujah"
Nolan punching out Varus Soleptor, doing what video game players have wanted to do for a long time.
And this is after Irisa's Big Damn Heroes moment, taking out several of Varus' men and enabling Nolan to deal with the rest.
During a prison fight over some food, Datak knocks out a Castithan woman built like a sumo.
In a really dark way, Stahma's ascension to Dragon-in-Chief is awesome as she puts Alak in his place, flat-out telling him that neither he nor his father are worthy to lead the Tarr family, and that the only reason she's keeping him around is to be a figurehead to the rest of the patriarchal Castithans.
Pottinger shooting down Datak's Batman Gambit is damned satisfying.
"Yes, someone like you could be very valuable to me... In ten years, when your sentence is up."
Nolan and Berlin saving Stahma from the second bomb, Nolan managing to disarm it at literally the last second. This is enough that the town, which for the most part was still holding a grudge against him for accidentally killing that Castithan kid last season, welcomes him back with open arms and cheers.
"The Cord and the Ax"
Alak calling out Datak for getting himself thrown in jail because he couldn't control his temper, topping it off with calling him a "miserable old bastard".
Datak waltzing back into his house like a boss, hopping in the bath and attempting to drown Stahma for leaving him to rot in jail.
Rafe, after finding out he's gonna be a grandpa, drags Alak aside for another awesome installment of "Rafe intimidates Alak Tarr".
Amanda beating the utter shtako out an abusive John is both awesome and disturbing. We've never actually seen Amanda take somebody on toe-to-toe like that, and it turns out that she's a brutal, efficient fighter... and she's also teetering on the edge of sanity due to Blue Devil withdrawal while she's doing it.
"Beasts of Burden"
After Datak scars Alak to teach him a lesson, Stahma gathers the boys to beat the ever-loving crap out of him and throw him in the street.
Alak himself; when his father attempts to force him into his own lifestyle by making him choose which of their loyal workers to kill, he instead tells Datak to kill him instead. Datak doesn't do it, but it's clear Alak wasn't sure if he would, and was willing to take the risk anyway; it shows that Alak might still be the man Christie thinks he is.
Crossing over with CMOH, the usually dry Doc Yewll is almost gentle when she assures Nolan and Irisa that she didn't tell ERep anything about their "Irathient godling," either under torture or as means of gaining a pardon. The fact that she's back to work and at least seems her old cheerfully-exasperated self again goes a long way toward making Defiance feel a little more... well, like home.
"Put the Damage On"
While suffering from visions brought on by a malfunctioning EGO implant, Amanda tosses her would-be rapist out a window (there was no one there) and fights off two more assailants later on (actually Tommy and Irisa). Crazy or not, she is not the victim she was when that incident actually happened.
"This Woman's Work
Stahma crusading for women's rights in her own, special way. Namely, by poisoning the wife and friends of religious bigshot Favi Kurr, and framing him.
Churchill fearlessly taking on the Gulanee with nothing a stick and a pistol. He fights well, but goes down in the end.
"If You Could See Her Through My Eyes"
Datak taking "An eye for an eye" to its logical extreme when he gouges out the bodypart-jacking doctor's eyes with his thumbs.
"Slouching Towards Bethlehem"
Kenya going Slave Leia on her captor by strangling him with her chains, and bashing his head in with a car hood. She doesn't get away, but props anyway.
There is just something distinctly...Stahma-esque about Stahma's interrogation, where she takes control and puts Berlin and Tommy off-balance with some well-aimed Passive-Aggressive Kombat and her Castithan sense of smell:
Stahma: Nolan. Such a...unique man. There's a certain air about him. Leather. Bourbon. Gun grease. Tommy: I'm sorry, but I don't really know what this has to do with our investigation. Stahma: Not a thing. Only Miss...Captain Rainier wears it well.
"Bottom of the World"
When Tennety tries to push Amanda around, reveling in the fact that Amanda's lost her position as mayor, Pottinger steps in and puts Tennety in her place by reminding her of her past crimes and the fact that he can prove she committed them, all the while getting some good digs in about how she's not as good as she likes to think.
The real killer of Deidre Lamb. Christie. When she sniffs out the fetus killing poison in her drink, she beats Deidre's ass and throws her from the top of the Arch. Stahma bursts out laughing when she deduces the truth, especially since she was planning on doing it herself.
Nolan's fight with Sukar. Nolan actually holds his own, even with Sukar being empowered by the Kaziri's nanites.
After Tommy is stabbed by Irisa, despite all their griping, Nolan takes the cargo sled off of his now-nonfunctioning car, straps the barely-alive Tommy on, and starts DRAGGING him back to town. Whether Tommy lives or not, Nolan's attempt is EXTREMELY admirable.
"All Things Must Pass"
Yewll shows how far she's come from who she was during the Pale Wars by flat out refusing the Kaziri's offer to be "saved" by it while it terraforms the planet, killing everything not aboard.
"Tell the Kaziri to shove her offer up her virtual ass."
Datak and Stahma taking revenge on their treacherous lieutenants by poisoning them, leaving them completely paralyzed, and then hiding them where no one will find them.
"I Almost Prayed"
Datak and Stahma saving Rafe and Berlin from a deranged E-Rep officer's firing squad. Berlin starts laughing hysterically at the irony of this.
Datak:[grabs Rafe as Stahma executes the sergeant in the background] Apologies. Family emergency. [leaves]
The Kaziri tries to retake control of Irisa by sticking her in a Lotus-Eater Machine where a vision of Tommy tries to convince her to make a deal to revive him. With some encouragement from Nolan, Irisa refuses the temptation and breaks free. We then get this:
Nolan: The Kaziri's trying to stop us. It's scared.
Irisa: It should be.
Irisa and Cai seizing control of the Kaziri and turning the terraformers back into orbit, obliterating the Ark debris field in orbit.
Even the backstory has one: The Defiant Few. When armies on both sides saw that the collateral damage from their battle was endangering civilians—especially children—they temporarily set aside their differences to rescue the civilians from damaged buildings. Even when their respective superiors ordered them to fight, the Defiant Few told their commanders where to stick it. Doubles as a Heartwarming Moment, and the incident is credited for starting the peace process.
Young Irisa, recently rescued from the cult, gets over her fear of knives and gains Improbable Aiming Skills in under 2 minutes.