Starting with the first mission, Zero Saints Thirty. The Saints team up with MI6 to hunt down and kill a known terrorist. After the events of the "Save Your Homies" ending of Saints Row the Third, Cyrus Temple could not stand the Saints being hailed as heroes, and plans to nuke Washington DC in retaliation. The Boss begins by rushing several guards and taking them out mercilessly while British spy Asha looks on slack jawed, and it gets better from there. After killing Temple the nuke is launched, and everyone is shocked as it looks like the Boss is doing a Heroic Sacrifice to stop it. Boss manages to grab onto the missile and disable it, in flight, while Aerosmith's Don't Want to Miss A Thing plays before it explodes. The Boss then flashes a thumbs up at the audience, before crashing into the Oval Office of the White House, and sitting in the President's chair, while the adoration of America, the Presidency, Keith fucking David and Benjamin motherfucking King is "Unlocked" for the Saints.Bad. Ass.
The South Portico defense mission doubles as this and a Moment of Funny: The Boss is blowing alien gunships out of the air by the dozen while doing ridiculous hand gestures and dropping Bond One-Liners all over.
What else do you say after shooting down an alien warship in front of the White House and jumping into its cockpit to fistfight a ten-foot-tall psychic alien warlord and being subsequently pinned down than:
The whole escape mission after the President wakes up from the simulation for the first time. After jumping aboard Kinzie and Keith David's spaceship, the President proceeds to pilot the ship while Haddaway's "What Is Love" song is playing. Epic.
The reveal of Johnny Gat's return is suitably epic. A low, panning shot of dozens of dead bodies, followed by the lone surviving Zin getting shanked through the skull with a combat knife, as Johnny casually recovers his glasses. "Fuck... yes." For thousands of fans who were hoping the gangster had found a way to cheat death, it was a moment worth cheering for.
In fact, the very reason Johnny's alive. During what appeared to be his death in SRTT, Zinyak had actually captured him because he feared Johnny'd single-handedly stop his invasion. Zinyak feared JOHNNY GAT more than even the President!
At the end of Shaundi's loyalty mission Veteran Child clones himself, take both Shaundis hostage and forces Boss to choose which one lives and dies. Both Shaundis go Fuck. That, overpower him, and old Shaundi shoots Veteran Child taking new Shaundi hostage and new Shaundi shoots Veteran Child taking old Shaundi hostage.
The licensed music played during key moments in the game help to add to the sheer amount of kickass this game packs. To list a few examples:
Aerosmith's "I Don't Wanna Miss a Thing", played at the end of the first mission when the Boss stops the nuke from destroying Washington DC.
Haddaway's "What Is Love", played during the mission where The Boss pilots a spaceship (with Kinzie and Keith David aboard) to escape from the Zin mothership.
Thin Lizzy's "The Boys Are Back In Town", played during Johnny Gat's loyalty mission, celebrating his return as he and the Boss enjoy some Genkibowl.
Stan Bush's "The Touch", played during the Grand Finale after the Boss dons power armor. The Boss and Zinyak reciting Optimus Prime and Megatron's dialogue from Transformers: The Movie makes it all the more awesome.
And Montell Jordan's "This Is How We Do It" during the soul train before the credits of the Good Ending.
The good ending itself is in danger of making one go blind from awesome. Not only do the Saints now lead the intergalactic Zin Empire, not only do they go on a drunken rampage through time, but they manage to save thousands of the best and brightest people Zinyak collected from Earth's history including the narrator of the story: Jane Austen. Oh. My. God.
A complete list of the time traveling shenanigans:
Johnny Gat explained to Columbus the Earth was round, worked for Attila the Hun, cut down Washington's cherry tree, pimped out the Trojan Horse, graffitied a dinosaur skeleton, stole the golden transcontinental railroad spike, scammed Custer with a life insurance policy, sabotaged a chariot race and took part in the shootout at the OK corral with an M16 assault rifle!.
Kinzie showed up Marilyn Monroe in a skirt, played Raquel Welch in Caveman days, and was the inspiration for the Lady Godivia's legend and had phone sex with Alexander Graham Bell.
Benjamin King helped build the pyramids, Shakespeare to write Hamlet, assisted the Vikings on their raids, boosted the wheels from the first car, and partied with Nero while Rome burned.
Shaundi was the original model for the Venus de Milo (it lost its arms when she accidentally fired her gun), was responsible for Leonardo cropping the Mona Lisa, vehicle surfed on the Wright Brother's plane, pimped out the first American flag and royally screwed up the world's animal population by sneaking all manner of monsters and mythological creatures onto Noah's ark.
Pierce dumped a basket of apples on Isaac Newton, graffitied the Great Wall, traded hats with Davy Crockett, inspired the story of the boy who held back the sea, taught the Knights of the Round Table roulette, gave Abraham Lincoln a punk rocker haircut.
Asha pranked the moon landings and fought the British occupation with Ghandi (using kung fu naturally).
Then the whole crew got drunk as hell and went on a dinosaur joyride.
Could one ask for a better ending?
The "Nuke" ability. When slamming into the ground from a sufficient height it causes an explosion so big the camera has to zoom out to show the entire city block just to get a good view of it. Bonus points for smoldering embers floating through the air afterwards and the ground being on fire where you landed.
Pierce has you fight off waves of demonic Saints Flow mascots, and a battle with a giant Saints Flow can named Paul ripped out of a Disaster Movie: first you fire rockets at his face, then you shoot at it from a helicopter, and then you fight it with a living statue. His Loyalty Mission has him pull of one of his over-complicated schemes to take out Maero and the Brotherhood.
Benjamin King relives the moment Tanya and the Vice Kings betrayed him. After running to the Saints church to find Julius, the Boss helps him wipe out the VK's, and forces Tanya to flee the simulation - and King's loyalty mission is all about making sure that Manipulative Bitch is Rewarded as a Traitor Deserves.
Asha has you aiding her in taking down your Evil Twin in one huge nod to the Metal Gear Solid series specifically, and stealth-based games as a whole. After kicking your own ass, you and Asha Double Tap yourself one more time for old times sake, and Asha flicks her cigarette on your evil corpse. Her loyalty mission starts off pedestrian with escorting a VIP, but quickly escalates to a high-speed chase out of a political thriller movie. And then Prof. Genki shows up, becomes Super Genki, and you both get to kick his ass with superpowers.
Volition letting fans see what Enter the Dominatrix (The DLC for the third game that would become this game) by releasing it as a full DLC for this game. As well as bringing back Donnie and Zimos, on top of that.
All throughout the XMAS DLC and not one ho joke. Since the series lived and breathed this incredible self control.