I think very few superhero costumes survive the translation from page to screen without becoming some degree of ridiculous. Iron Man has probably worked best, because his costume is a technological battle suit, and the bright colors fit Tony's personality as depicted in the film. Cap's WWII suit is just this side of believable because they grounded it so thoroughly in something that looked like it might be a commando uniform of that era. The modern-day Avengers variant is less successful in that respect. Thor is...Thor. If you're buying that Asgard and it's inhabitants exist, then I guess they can wear whatever the hell they want, however chuckle-worthy.
Superman and Batman and Spidey are just silly in person. Why does Batman have a cape? I know, he uses it as a glider occasionally, but isn't it a hindrance most of the time? Doesn't the cowl obstruct his hearing and peripheral vision? Doesn't it get hot? Don't the pointy ears reduce his head clearance in tight situations?
Supes is invulnerable and super-everything, so I guess wearing a cape won't hurt him, but then you wonder why he wears it at all. Are the cape and underpants and red booties some sort of Gaga-esque affectation?
Spidey's formfitting bodysuit makes some sense, but the color and design certainly works against stealth. Also, as was brought up elsewhere, the gloves and boots would seem to be an impediment to his sticktoititveness.
