A little bit of a different type of game and I'm cheating by using four moments, but they all stuck with me.
Not For Broadcast, Day 296: The Heatwave.
It starts off with a slight shift in tone from the earlier broadcasts, you feel the tension ramping up, and then you know exactly what's coming, but it's still a fucking gut punch no matter what choice you make.
Day 371: The 20 Week War adds on to that with this underlying tension from the last broadcast, broken by some hysterical nonsense and then hits you with a sobering end to the broadcast which plays out three different ways depending on earlier decisions you've made. All three are devastating in their own right.
The entirety of Day 2602: The Finale is just fucking wild, and best experienced without any hint of spoilers.
Beyond that, the lockdown broadcast is fucking hilarious and came out of nowhere. The sheer absurdity of it caused a "wait, what the fuck is even happening?" moment every single time something new happened.
Honestly, that entire game has so many of these moments, but those are the ones that have stuck with me. I often find myself singing "Mr. Bear (What's That Over There?)" for literally no reason whatsoever.