Most-noticably, Cap seems to have undergone a major “modernization” on his outfit: Traditional cowl with “pronounced” wings rather than the helmet/decal look of the WWII-set movie, sleeker material in general and the torso-stripes are now just “there” instead of being part of his gear-harness. I like it.
Iron Man is either wearing the older-style armor or a new suit with the “classic” circular chest-plate.
No “costume” in the traditional sense for Hawkeye, he’s basically wearing his “Ultimates” gear. Bit of a mistake in my estimation – the lack of visual-“flair,” however practical, only reinforces how small/limited he looks next to The God, The Walking Tank, Shrek and The Perfect Human. (Black Widow’s “flair,” obviously, came bundled with the actress…)