1. Captain America: The Winter Soldier
Captain America: The Winter Soldier revealed that S.H.I.E.L.D. was compromised since it began and that HYDRA had been growing inside the organization the entire time. Unsure of who he can trust, Fury turns to Steve Rogers, providing him with enough information to start looking into it before being assassinated.
The information puts Steve on a collision course with the Winter Soldier, a HYDRA assassin, who he discovers is his old friend Bucky who he believed died during World War II. We learn later that Fury faked his death as a way to gain the upper hand and, after realizing that there’s no way to salvage S.H.I.E.L.D., brings in a close circle of Steve, Natasha Romanoff, Sam Wilson, and Maria Hill to bring down the entire organization.
The Russo Brothers brought a grounded tone that felt unique to the franchise at the time and would later be the basis for several future projects. It’s also responsible for providing some of the best action in the MCU, including an epic car chase sequence where Fury escapes a squad of HYDRA soldiers posing as police officers.
It’s one of the best sequels the MCU has put out but also one of their best films overall which is even more impressive considering it doesn’t feature any cameos or set up any overarching storylines.