The one at the start of lone wolf. It's short but it does what it needs to really well. It shows a beaten, lost soldier making his last stand against his enemy. He knows he's not going to survive, so he's going to take out as many covies as he can before he goes down.
The one after Jeorge dies. Walking through alone through the crash site and sneaking into the city just makes the spartan look bad***. Plus I remember just the feeling I would get somewhat somber like wow
I've always liked the cut-scene when you are at the relay in the first mission and while Jorge is talking to the civilian chick, Noble Team gets ambushed by Elites. And you get that first person POV with the Elite knocking you to the ground and gets right in your face to stab you before you punch it and it flees with a hostage. That music that kicks in at that moment also ties in very well. Not sure but I have just always like that cut-scene.