I saw this one later, I'm not sure whether it before Winter Soldier or after, but it was certainly post- The Avengers. I ended up loving it. From the design of the 1940s era sets and costumes, to the action sequences, and even the romance between Peggy and Steve is the best of the universe. The effects to make Chris Evans look to be the scrawny kid from Brooklyn alone still boggle my mind every time I watch it. The chemistry between him and Bucky is great, as is the chemistry between him and the aforementioned Peggy Carter. Dominic Cooper's Howard Stark also manages to stand out from the cast. This movie makes Captain America, a character that should appear as corny or anachronistic, just as cool as Tony Stark or Thor. He's relatable, a feat not easily accomplished for a chiseled do-gooder. Yet it's that purity, and hope within Cap that we want to see within ourselves. He's not lecturing the audience on how they should live their lives, but trying to be the best human being he can be. He's maybe overly patriotic, and unrealistically good natured, but that's okay because you believe in him and you cheer for him.
As for his nemesis, Red Skull. Hugo Weaving does a good job portraying this character that uses the political machinations of the Nazi party for his own selfish scientific pursuits. The part where his mask is removed to reveal his titular appearance works really well, once again proving the prowess of the effects team in this film. While he doesn't have the personality or complexity of a Loki, Hela, Killmonger, or Ultron, he's still diabolically menacing. This might be the most important of the Phase One films leading up to The Avengers. It's here that you're introduced to Peggy Carter and Howard Stark prior to their forming SHIELD. I thoroughly believe Cap and Peggy is the best written romance in the universe. I would have liked a few more scenes with Howard and Steve, which would make his future relationship with Tony and the revelation of Civil War that much more important. Their interactions with Cap influence their lives for better or worse throughout the history of the universe. That's not to mention Bucky's impact on the universe, or even Hydra's, but we'll get there. That past is just as important as the present, and The First Avenger demonstrates that perfectly.