While explaining the Pilgrimage to Chief, Tali gives him an anecdote about how Kal'Reegar brought home a Brute Gravity Hammer as a gift to the Rayya's Captain. Reegar was reportedly very injured in the process of acquiring it, and when Chief asks exactly how he did so, Tali says that he laconically replied "It wasn't easy."
Chapter 17. Chief has been kidnapped. Less than thirty seconds after he's been dumped into a van, an individual who wants him freed is not only on the case, but has cornered the one who drugged Chief, executed her, and figured out where Chief's squadmate most interested in stopping Saleon is. And the best part? It's the Arbiter, still alive and still as deadly as ever.
Chief's response to said speech and beatdown is pretty awesome as well: the second Saren gets close to deliver the coup de grace with his pistol, he swiftly and painfully learns that for all his biotic power, physically he's a Badass Normal against a Spartan II. In one short paragraph Chief decisively ends the fight.
Pretty much all of Chapter 31. We get a huge battle sequence with Saren's army vs. Forerunner Knights vs. The Flood vs. Master Chief's squad, the first three of which team up to take down Chief and co once he's rescued. They get curbstomped. And then, to stop Saren from getting away, Master Chief performs the Mass Effect equivalent of a Fastball Special, with help from Liara. And to wrap things up, after Saren gets away, the squad madly dashes back to the Normandy with the looming prospect of a radiation induced implosion of the Registry hot on their heels.
Chapter 33: There are Vanguard Hunters now and it's as awesome as it sounds.
They're back in Chapter 40. And kill a Geth Colossus without taking a scratch.
When confronting a small army of Rent-a-cops at Lorik Qui'in's office on Noveria, The Master Chief uses equal parts Badass Boast and The Long List to explain all the shit he's been through in his life up to this point and then asks them if they expect to do any better at killing him than The Covenant, Flood and Geth did. After pistol-whipping Stirling, who still likes her odds, thinking the Chief isn't the real thing anyway, the guards not only flee, but half of them wait patiently at the elevator because the other half leave without them.