Marvel has done a great job with these two movies. Both the story and animation is well done.
Ultimate Avengers I (2006)
In 1945, Captain America, U.S. soldier created with a Super-Soldier Serum, is fighting the Nazis during World War II, and after averting a nuclear disaster, he falls into the icy waters of the North Atlantic, and frozen in suspended animation, only to be revived in the twenty-first century by the American military, who are hoping that they can recreate the serum in Captain America's blood in order to create more super-soldiers. But now, with the world facing the very same evil, Captain America must rise again as our last hope of survival, and lead a strong-willed team of today's superheroes.
Ultimate Avengers II: Rise Of The Panther
The mightiest of heroes the ultimate Avengers must continue their war against the same aliens they fought. This time, the aliens and Captain America's old enemy Herr Kleiser (the alien shape shifter who supposedly died in 1945), are invading a hidden city in Africa, where the Black Panther is king. But when Kleiser murders the Black Panther's father T'Chaka, Black Panther travels to the U.S.A. to get advice from Captain America. The Avengers must travel to Africa, where a bloody war will be waged against the invading aliens.