Retcons can go either one of two ways when it comes to comic books - the right way, or the wrong way. Fortunately for a great many heroes past and present there've been quite a few that have changed them for the better, ditching a dated motif for something decidedly more compelling, whether that be a design, or even an entire personality.
Equally, there have also been comic book moments that have redefined the way we've looked at certain characters, ones once considered pretty terrible. 'Terrible' in this instance can be used to denote a genuinely horrible character - someone you wouldn't consider a hero at first - or a poorly thought-out concept which, when compared to other characters, didn't age spectacularly.
This isn't an exclusive concept for either Marvel or DC either, with both companies having played host to some truly wonderful reappraisals of their characters, whether that be a carefully orchestrated retcon, or through a remarkable story that managed to change the way readers approached a given hero.
It might not happen all the time, but when these stories come along, they manage to change perceptions in no time at all.