It works so well because at this point we're wholly invested in these characters and, as mentioned, the motivation was clear and unwavering from the jump. Nobody gave a flying fart about Bats and Supes fighting because we were never given a reason to care, let alone any kind of sensible explanation. Even if you walked into Civil War cold without seeing any of the other MCU movies, you get why they are fighting on a few levels.

Downey and Evans put on some damn fine work here