The ATLA finale was all about death, and the fear of death, and the tragedy of family conflict, and a butting-against-heads of ideologies (kill or not kill)
There was just SO MUCH going on between the characters in those episodes. When Ozai started burning the world, I felt fear. When I saw Sokka apologizing to Toph for their impending deaths hanging off the airship (and Toph got all teary eyed) I got sad. When Zuko took the hit for Katara, I was stunned. When Azula freaked the fuck out after getting chained up, I was sorry for Azula AND disgusted. When Aang hid in the rock ball, I was super tense. When he went into full badass Avatar State, I was overcome with the raw power. Same when he fought for his soul when energy bending Ozai. I felt really relieved when it was all over, everyone was crowned, and the camera zoomed off into the sky.
In this... I felt a bit tense when Mako was zapping the heart, and was slightly worried he might not make it. And the rest of it was just me hanging out, watching.