The Non-Spoiler review: Go see it and enjoy it, it's everything Avengers: Age of Ultron should have been and more, and ties up a lot of loose ends from Captain America: Winter Soldier to boot.
Our movie opens with some unfinished business: HYDRA agents in 1991 programming the aforementioned Winter Soldier (Sebastian Shaw, who was once Cap's faithful sidekick Bucky) to "sanction and retrieve" a target. He is ruthlessly effective, and the mission will have great repercussions 25 years later...
...which brings us to Lagos, Nigeria, present day. Captain America (Chris Evans), Black Widow (Scarlett Johanssen), Falcon (Anthony Mackie) and Scarlet Witch (Elizabeth Olsen) are tracking down former HYDRA mercenary Crossbones (Frank Grillo) to a chemical weapons lab. The mission is going well until Crossbones drops Bucky's name and Cap, distracted by the news, almost gets half of a crowded marketplace blown to pieces.
As it is, the dozens of casualties are one international incident too far for the United Nations to continue to stand back and let the Avengers operate without oversight. General "Thunderbolt" Ross (William Hurt) drops a rather large set of United Nations accords on the team and says sign, or else. Iron Man (Robert Downey, Jr.), Vision (Paul Bettany), War Machine (Don Cheadle) and Black Widow all decide doing so is a good idea. Cap, Falcon, and Scarlet Witch do not.
But when the Avengers once again fail to stop people from getting killed at the accord signing ceremony, and Bucky is the prime suspect, everything goes to hell rather quickly. Cap is willing to bet everything that Bucky is being controlled again, and he wants to find out who is pulling his strings. Iron Man is sent to bring Bucky in, especially since the attack at the ceremony kills the King of Wakanda, leaving T'Challa (Chadwick Boseman) as the new monarch and protector of the African nation, the Black Panther.
What results is a fight long brewing between the Avengers and their allies in the wake of the most recent Marvel films, and it's worth every penny, particularly the fight scene that you know is coming from the opening scene, and behind it all is a secret long buried in the past...
The SPOILERS (you have been warned!) start after the jump.