I had a great time with this, it narrowly surpasses 'Iron Man' for me.
'Captain America: The First Avenger' is thoroughly entertaining. I absolutely enjoyed the story and how it is told, while the 1940s style is done fantastically - love the settings and costumes. The only negative I have is about the body double effect of skinny Captain America - which looks, honestly, ridiculous... in an amusing way, at least.
This is, possibly, the most I've enjoyed the overall cast for an MCU film so far. Chris Evans is fun to watch in the lead role, he does a grand job. Behind him, the likes of Tommy Lee Jones, Hayley Atwell and Hugo Weaving are enjoyable too.
A very pleasant experience, this. Good fun.