im very impressed, as a first flash this i one of the best quality sprite movies i've seen in a long time.
The audio was near perfect, with the only problem i had was that some sfx was a bit loader than the average volume, there was one too many sfx foot steps for Captain America, but overall perfect. most people dont put in half as much work as you did, you nailed it man.
Background design was simple and effective.
Style was good, i liked how you placed everything so it's like watching from a tv or a gameboy advance mini.
Animation/directing was good, the sprites had good follow.
Story; well can't really say, the dialog had style in presentation, but maybe place the dialog in word bubbles or maybe use the space at the top for a dialog box like in RPG's to make it a bit easier to read.
Overall very good, your already better than most of the people on NG's and i personal know your heading in the right direction. I hope to see some really great things from you in the near future.