Word of God from chapter 7, on Garrus: "As you may have noticed, Garrus is a bit...different. This is kind of what happens when you take someone whose solution to uncontrolled crime and restrictive police procedure was to become Sniper Batman and give him free rein to prosecute crime his way - without providing the baseline sense of restraint that a police force would instill. You get, well, the unholy fusion of turian Jack Bauer and the Kool-Aid Man."
To elaborate: When Garrus needs to grab a guy to interrogate him, he hijacks a C-Sec tank and blows up his car right after he gets out of it. When he needs to drop in on a mercenary hideout, he crashes through the fucking wall with giant cargo hauler and kneecaps everyone. When the above mercenaries have six such hideouts, well, he does it six times, to equal success everytime.
And to cap it off? When he needs to return to the first hideout, he crashes through the wall again. A different wall this time, with the first hole still clearly visible from his point of entry.
One of the very best is at the end of the fifth chapter, where Kane makes his triumphant return after a hundred and fifty years by cutting off the Council in the middle of one of their speeches by hijacking the holoprojector in the Council Chamber.
The response to the above as well. Almost every review posted had some form of "KANE LIVES!" written in their reviews.
Jenkins gets one when he kills eight geth in about as many seconds, including a Destroyer, in close combat. Then Saren kills him by scrambling his targeting and releasing the buzzers.
Sovereign has a moment when it faces off against a GDI ion cannon array that is described as being able to destroy the most powerful dreadnoughts in anyone's fleet. It actually outmaneuvers the arrays and ion cannon satellites around Eden Prime by bombarding them at a distance and then forcing them to expend their shots at a distant target, and the jumps into FTL right before the beams reach its position. The array in question dumps all its capacitors into the guns to recharge instantly, and delivers a point-blank blast into the Reaper - which Sovereign shrugs off, suffering only superficial damage, and then clinically destroys the array before moving on.
Zaeed's approach to a warehouse full of mercenaries. Blow open the door with a carbomb and then march inside piloting a freaking Wolverine with guns and grenade launchers blazing.
Zaeed, in his Wolverine mech, attempts to grab the Quarians for the Shadow Broker. Shepherd is in a Mexican Standoff with him and Jacob's men are too far away. And then Alenko shows up, lifts his two-ton REV12 in the air with his biotics, and then chucks him out of the room with his bare hands. Big Damn Heroes indeed.
As disturbing as what happens afterward is, the entire scene where the turian cruiser Valedictum is utterly overpowered by the Scrin warship, which casually curbstomps it and takes over its crew, serves as a stark and impressive display of just how powerful they are.
Two random C-Sec officers in a tiny, lightly-armed aircar witness the Scrin opening fire on civilians. Do they take cover and call for backup? Hell no. They load some high explosive rounds and open fire on the Scrin in a display of lunatic bravery that gets the amazed approval of both Admiral Parker and Miranda Lawson.
Even better, they keep going like that for a while, dodging Scrin fire like madmen. Sadly, Reality Ensues, and they are killed by a Gunwalker, but not before they see a GDI Orca take out the Gunwalker. Their badassery is solidified when the last words of the C-Sec gunner are "We won" and the Orca Pilot calls them the "ballsiest C-Sec officers she'd ever seen."
Garrus Vakarian, the only turian so insane that the Scrin actually attach a qualifier to his designation labeling him as Crazy Awesome. Solidified when, as Shepard and Co are getting overwhelmed by a Corrupter, he blows open a wall next to it, steps through while duel-wielding Werewolf submachineguns, blasts massive holes in the side of it, and chucks grenades into the creature's wounds before diving for cover.
How Crazy Awesome is Garrus? He does an Unflinching Walk. Towards a Scrin Battlemind. Ignoring aircars being thrown at him. And he chooses to stand still and take the shot, even when he sees an aircar being thrown at him. It's either shoot or evade, and Garrus willingly chooses "shoot."
"Then KalíReegar came around the corner opposite the Scrin, having gained half his bodyweight in gun."
To expand on this, the entire scene leading up to this moment has involved Shepard holding off Scrin warriors, first a Ravager that took an entire magazine of grenades to put down. Then a Corrupter shows up, and Shepard burns through another entire magazine and doesn't even do much more than annoy it because of its regeneration. Then, as she and Tali and Michel are trying to escape the unstoppable juggernaut, Kal'Reegar comes around the corner packing a four-barreled railgun so massive he needs a strength-assist frame to carry it, and blasts the Corrupter off its feet.
And while he delivers a one-liner before opening fire, it's not anything witty, but still completely awesome.
For a while... the Scrin Battlemind has proven utterly impervious to all attacks. It has shrugged off railguns, mass accelerators, biotics, and other esoteric weapons, until finally it starts to wear down. But who delivers the killing blow? Shepard, the survivor of a previous Scrin attack? Garrus, who we've already mentioned is kind of all of the awesome? Kaiden, the Tiberium Mutant Biotic? Admiral Parker, the identical grandson of Havoc? Anderson, the grizzled old soldier? No. Udina- yes, THAT Udina- takes a car and RAMS THE HELL OUT OF THE BATTLEMIND. He then shrugs it off and says "Old spacer trick- as long as you've got engines and the bow, you've still got one weapon. Figured it would work the same with aircars." Congratulations, Peptuck, for taking one of the most reviled and annoying characters in the Mass Effect universe, and with one action, made him utterly badass.
In addition to this, Kal'Reegar ends up taking a kinetic blast from the Battlemind, and is given up for dead. And then he gets up, has his suit tend to his wounds, and he walks back into the fray. "You can't kill me."
Whenever Kaidan uses his superstrength, really. At one point he essentially beats the shit out of a Scrin Intruder by shoulder-checking it, blowing its head apart, body-slamming it, and stomping on its chest until its armor breaks and he can pump bullets into the prone body. Later, he saves a couple of civilians from a flying aircar by hitting it with a biotic pull and then punching it out of the way.
James' reaction to a Ravager dropping down right next to him is to do what comes naturally. Kick that pendejo in the face and shoulder check it into a wall before hopping on its back and blasting it point-blank with a shotgun.
Liara staring down Wrex and talking him into staying to defend the scientists.