Much as the title of the upcoming X-Men film does ("Days of Future Past") does, "The Winter Soldier" gives away the plot of the film, as it is the same as a well-known storyline in the comics.
In this trailer (no. 2), we get to see Captain America's new partner, the Falcon, in flight. No, he's not played by Will Smith, as some comments on YouTube asked, but instead by Anthony Mackie. In the comics, the Falcon did not fly originally, but later was gifted with a flying harness by the Black Panther.
In the comics, the "Winter Soldier" storyline was designed by Marvel to bring back Bucky Barnes, who had been long dead after dying in the accident that ended up freezing Captain America in hibernation until the Avengers found him. The fact that the movies would resurrect Bucky was made clear by the fact that Sebastian Stan was signed for multiple movies.
In the comics, Bucky Barnes resurrection is described as follows:
After the plane explodes, General Vasily Karpov and the crew of a Russian patrol submarine find Bucky's cold-preserved body missing one arm. Bucky is revived in Moscow, but suffers brain damage with amnesia as a result of the explosion. Scientists attach a bionic arm, upgrading it as technology improves."Captain America: The Winter Soldier," is set to hit theaters on April 4.
Programmed to be a Soviet assassin for Department X, under the code name the Winter Soldier, he is sent on covert wetworks missions, i.e., missions involving assassination, becoming increasingly ruthless and efficient as he kills in the name of the state.