Second, I feel there are two major interesting aspect of Cap. One is his time displacement, and the other is his legacy as a super soldier. I feel that the time periods are better from a general view, but also needs more time to be really interesting and to be done well. I don't want the Avengers movie to be cap waking up having a few scene of "Woe is me" and then jump right into action. I think Fury would let Cap retire, not force him into a fight. And I think it's really important to get this character development right. To see things as he sees them, to go through this journey with him, to see him compelled to take up the shield again and find his place in this new world as it's protector. This "man lost in the modern world" story will be lost and we will lose the most interesting aspect of the character.
My third and final reason is that the Avengers movie will already have a tin of A–list actors and the potential for great interactions, but they will have to cater to Cap and his story. The Avengers movie should be about the team, maybe two characters have more focus, but they should dominate the screen. I don't want all these great characters to become glorified cameos. It should be cap, the unsure leader, Tony, they party boy who's more of a loner, Thor, who's against the very idea of a government super team, and Pym, the jerk. I feel these interactions would work much better if the film didn't have to go into Cap's revival.