What really sells it is Issac's words before the boss fight. Faced with the biggest goddamn necromorph he's ever seen, he utters a simple and quiet sentence, showing us that even after all the horror and abuse he's gone through, Isaac Clarke is not going down without a fight.
The descent onto Tau Volantis is a noteworthy moment too, especially in cooperative.
Isaac's Eleventh Hour Superpower near the end, activated by stepping on marked plates on the ground. It powers his Kinesis and Stasis, to the point where he can rip off limbs from still-alive Necromorphs and slow them to a literal crawl.
After Ellie is killed by Danik's intervention, Isaac finally loses his cool. While he isn't screaming incoherently, he outright states that his only goal is to take down everyone and everything responsible for the necromorph plague... even if it kills him. The entire next chapter consists of one long rampage through Unitologists and necromorphs alike, as you pursue Danik into the bowels of the earth. A full swarm of necromorphs, an entire company of Unitologist troops, and even the hulking new alien necromorphs fail to stop you, all culminating in a vertical chase sequence where you battle all the aforementioned threats while rappelling into an abyss. According to the Unitologist radio chatter, they're more afraid of YOU than the undead horrors pouring out of the woodwork!
It's also worth mentioning that for most of the series, Isaac has only been fighting in self defense. This time, he's launching a one (or two) man assault on the people and monsters that have made his life a living hell.