I wasn't expecting a lot from Captain America. I disliked star Chris Evans in the Fantastic Four and advance hints about the plot were not encouraging. My wife expected even less. She knew nothing about the character except that her brother likes him.
The movie was a pleasant surprise. It is very enjoyable. Like Iron Man, some of the best parts come before the action when we are watching Steve Rogers. The German scientist Dr. Erskine, who creates Captain America, is also fun to watch.
An interesting thing about this movie is how firmly it is embedded in the Marvel Universe, even though most of it takes place decades ago. I'm going to examine this with lots of spoilers. You have been warned.
When we first see the World of 1938 exhibit there is a glimpse of a figure dressed in red under a bell jar. This is the original Human Torch (who was actually an android). Howard Stark is either the father or grandfather of Tony Stark although the character is based on Howard Hughs. The movie opens with a few mentions of Asgard and Odin as the Skull seizes the Cosmic Cube.
What we think of as Marvel only published a few stories of Captain America during WWII. The company was called Timely in the 1940s and the style of stories written then does not lend itself to modern movies. The film-makers cheated a bit by combining Captain America with the WWII comics that Marvel actually did write - Sargent Fury and his Howling Commandos.
A side note here - Stan Lee and Jack Kirby had been doing the Sergent Fury comics for a while when the secret agent craze hit. Rather than create a new character to be a secret agent, they reused Fury, making him head of SHIELD. At the time it was quite reasonable that WWII sergeant could have risen to colonel and be chosen to lead an elite operation. The timing no longer works since the modern Fury would be in his 90s (in the comics it was explained that he was given a longevity drug).
What we end up with is Captain America doing double duty as himself and as the replacement leader of the Howlers. It makes more scense than the original comic books.
One place where this melding happens is with the Red Skull and Hydra. In the comics, the Hydra was founded by a villain from Sargent Fury and the Skull a Captain America villain. In the movie, the Skull is the head of Hydra. Also, during WWII, the Skull was just a regular person with a skull mask. His face was deformed after he was transferred into a clone of Steve Rogers, complete with Super Soldier enhancements.
Hydra itself is an interesting addition that I am sure was put in for the international crowd. The movie makes it clear that Captain America is saving Germany from Hydra along with the rest of the world. In fact, the movie completely glosses over the evils of fascism. This is possibly its biggest flaw. I assume that this was done for the European audience. At least the movie never lapses into Superman territory (Truth, Justice, and all that).
One big change between the comics and the movie is the character of Bucky Barnes. In the comics Bucky was a costumed teen-age sidekick. In the movie he is a full-grown adult and Cap's best friend.
It is jarring at the end when Cap is confronted by the 21st century. The character only frozen for 20 years in the comics but nearly 70 years in the movies. In the comics, Cap replaced his WWII sweetheart, Peggy Carter with her younger sister. Now he could be dating her granddaughter.