They managed to put 6 foot tall human infantry next to 20 foot tall Autobots and convincingly portray them as Bash Brothers. Special props go to the guy who jumped on the back of Shockwave.
Optimus taking down all the Decepticons in various ways while a variation of Mind Heist plays. This scene can be found here.
Brief as it was, it was amazing to see the Autobots fighting Sentinel as a unit with NEST.
The united Autobots and humans racing down the streets of Chicago into battle.
Ratchet putting up a hell of a fight as he's forced to the ground, and still snarling at the Decepticons to frag off when he's on his knees.
Optimus Prime VS Sentinel Prime. Prime VS Prime smackdown. Awesome doesn't even begin to describe it.
Doesn't anyone else think that Sam taking down Starscream all by himself was just a little bit FUCKING BADASS?
Carly managing to talk to Megatron, and not only surviving, but she talks him into killing Sentinel. Not bad for a Replacement Scrappy.
Not to mention insult him to his face, only for him to realise she's got a point.
A Meta Example: This film is now the fourth highest grossing film of all time, despite being one of the most flamed films ever. Critical Dissonance FTW!
Optimus finally deciding that enough is enough, and tearing off both Megatron's HEAD AND SPINE. WITH ONE ARM. That moment, arguably more then any other in the entire series, establishes Optimus as an absolute BADASS.
And just before he does it, his face-guard pops up to cover his mouth, making it as close to the original Optimus putting Megatron down permanently as we're ever likely to see.
The dialogue in that scene really sells it too. Megatron boasts "Who would you be without ME, Prime?" Optimus has had it. He knows Megatron will never come back from the atrocities he's done. He's pointing a gun at him while suing for peace. Of all the times in the franchise Optimus has let Megatron get away, had him escape, or never just shoot him this is it. Optimus is done with Megatron and now decides it's time to live his life without his eternal foe. Megatron won't get away this time.
Ironhide's arrival into that fight was a CMOA in itself. He comes tearing in at full-speed in truck mode, rams both Decepticons in a head-on collision which causes him to flip over them, transforms to robot mode in mid-air, and lands on his feet with both guns already drawn and cocked at the Decepticons' heads.
To save everyone the trouble...because we'd be hear all day listing this...but pretty much ANYTHING Bumblebee and Optimus did!
Colonel Lennox and a strike team of about twenty or so humans, working together without any vehicle or Autobot support, take down Shockwave (though it takes the Autobots and Optimus to actually defeat him), Barricade, and four other Decepticons on foot, using nothing but accurate sniper fire, parachutes, and sheer balls.
Not pictured on-screen; several years of refining their tactics by fighting Decepticons. Think of all the bullets fired, blood shed, and lives lost.
For those who haven't seen it and wished to be spoiled, Sam knocks Dylan Gould into the Space Bridge Pillar (electrocuting and killing him) with an iron pipe he picked up off the ground after saying this! It was, pretty much, Sam's response to Gould, who was basically giving him a Hannibal Lecture, "You think you're some kind of hero?" To which Sam replies with the above quote.
Optimus Prime. Buzz Aldrin. Meeting one another and, with the utmost humility and sincerity, saying that it is an honor.
Optimus Prime finally defeating Megatron for good.
Prime's trailer. We've been waiting for it for two films and it doesn't disappoint. Not only does it turn into a badass flying harness, but, like the original, it opens up into a base... which is fully stocked with dozens of weapons.
Starscream's back to being dangerous in DotM. He drops down from low orbit to shoot down the Autobots' spaceship and later leaps off a building and shreds the Ospreys transporting Lennox's team with his buzzsaw hand. Also serves as a Call Back to his F-22 Stepping Stones in the Sky moment in the first film.
Bumblebee killing Soundwave. He overpowers Soundwave and his Mooks, then jams his arm cannon into Soundwave's chest and blows his head off through his chest! Made even better due to the fact Bumblebee is shown mourning the death of Wheeljack at Soundwaves hands and now has avenged his fallen friend.
The novelization adds a little one for Ironhide. Whereas the film had him & Sideswipe engaging the two remaining Dreads in a gunfight, the novel has five Dreads charging at the NEST base. Ironhide simply transformers, stands in their path, and becomes The Immovable Object, letting the 'Cons literally crash into him. Each of the Dreads is killed on impact, while Ironhide simply withstands the hits with little more than some scratches and being knocked back a bit. He then casually brushes Decepti-parts off of himself and quips "They just don't make them like they used to".
When the Autobots return for the final battle after having been thought destroyed with their ship, Optimus delivers what may be the single most badass line in the entire franchise:
Optimus: We will kill them all.
It's the way he says it more than anything.
The novel also adds a Dying Moment of Awesome for The Twins. Skids dives in front of a shot fired by Sentinel Prime at Bumblebee, saving Bee's life at the cost of his own. This causes Mudflap to fly into an Unstoppable Rage and charge Sentinel, dodging the traitorbot's shots, tackling him to the ground, and pummelling him as hard as possible. It does little harm to Sentinel, but it does give the others time to escape, and as Sentinel blasts him, Mudflap continues to attack him relentlessly even as he is literally disintegrating. Sentinel even mentions that Mudflap died a death worthy of an Autobot.
Basically anything the Wreckers do in the final battle. Really, there's no way that a trio of weaponized race cars tearing down the streets blowing up everything in their path can't be insanely cool.
Three words: "Wreckers...kill him!". The sheer brutality that the trio proceeds to unleash upon the pilot of the downed Decepticon fighter is practically a whole brand of badass unto itself.
Lennox and his team get his fair share of awesome in the movie.
Lennox: Listen up! If we wanna hit back, we're gonna have to wingsuit in. It's the only way to get close. I can't promise anyone a ride home, but if you're with me... The world needs you now. Soldier: [steps forward]...I'llfind my own ride home,sir. Lennox: [nods appreciatively] WHO ELSE? [The rest of the soldiers step up and shout their commitment to the mission]
Sentinel basically duels Optimus, while being shot at by NEST soldiers, and while smacking away the other 7 Autobots whenever they try to interfere. In short he fights all the good guys at once by himself and hold his own. It ends with a CMOA for some random unnamed NEST soldier, who pegs Sentinel with a rocket just a he finally pulls out the dreaded rust gun he was able to kill Ironhide with, causing Sentinel to lose his gun, and for him to fall back. Optimus pursues however and the Awesome goes back to Sentinel, who, one on one beats Optimus in a duel and would have basically won without Megatron suddenly interfering.
Upon rewatching the movie, I found that Optimus has a very efficient way of dispatching foes that works out quite awesomely. He uses said tactic to kill Shockwave and Megatron with deadly efficiency. Both Shockwave and Megatron fire at Optimus as he moves towards them. Optimus dodges both moves and hits his opponent in the chest (with a gunshot in Shockwave's case and his axe in Megatron's) which stuns them momentarily. He then uses that opening to deliver the set-up blows (punching out part of Shockwave's torso then slugging him in the face and choke slamming him or kicking out Megatron's knee from behind) and then delivers the killing blow. It's quite awesome to see the tactic play out.
The humans launching a Macross Missile Massacre against the Decepticons from far enough way that it takes the better part of a full minute to show the missiles' flight into the city, opening up the battle proper.