Today's superhero I liked as a kid because I thought his costume was cool is the Silver Age Green Lantern. Green has always been a favorite color of mine, so I'm sure the blatant simplicity of his color scheme was a draw. But what I think also struck me was that, while his leggings and sleeves gave the impression of being black, they were as often as not colored in greys and purples with heavily spotted blacks. The white gloves proved an interesting contrast to both the black sleeves, as well as the green boots.
The spotted blacks were also emphasized by the fact that his power was light-based. That meant that he was frequently depicted with bright lights and strong shadows. Less so outside the Neal Adams comics I grew up on, but there were still some strikingly lit panels from Gil Kane and the like. Certainly moreso than you could find in a typical issue of Action Comics or World's Finest.
GL was also unique (at least to me at the time) in that he didn't have a belt. He was clearly wearing more of a body suit, cowing even less to the conceit that a spandex costume might be practical in any capacity. Like Aquaman, he stood out against fellow Justice Leaguers by being the only one who's costume did not comfortably split at the waist.
My only real complaint of the costume was that the chest emblem was crudely designed. The squared off top and bottom never really fit with the concentric circles. That said, I think some of the later insignias have been a bit over-designed and I can now better appreciate the Silver Age charm of the original's clunkiness. But, at the time, I wasn't overly keen on that one aspect of the outfit.
But the rest of it was slick, I thought, and I was quite excited when Hal Jordan started appearing on Super Friends.