I mean first the Grey is the the smallest of the four, and already that's something, it tells you that the guy isn't about physical confrontation. His outfit resembles a robe, and it's got gold on it, and again, that speaks to something, that evokes a religious leader of some kind, but more importantly it's a point of interest. It's things that catch your eye, and that make you wonder about the kind of dude he is.
Same for Killer Croc, beyond the fact that he's big and huge. There's the bare arms, and the orange lines in the outfit, all putting the emphasis on his musculature. You immediately get that he's physical, that he's come to fuck shit up.
I mean shit, you can even look at Corvus Glaive on the far left, and you see an older, leaner guy, whose clothes seem to be in tatters, and you kinda get instinctually that this is a guy who has been at it for a while. The weird spear even tells you that he's an expert at some kind of alien combat technique.
And, I'm not even saying that because I know those characters, this is just stuff that people can immediately infer from looking at them, which is what design is here for.
Meanwhile let's take a look at Proxima Midnight:
-Uh she's blue
-She's got a generic space armor, which doesn't even seem to have any kind of flair
-She's holding a spear
There isn't really any story that's being told, aside from, well this is a lady that fights in space with a spear.
Again, when I say "interesting", I just mean "that, in any way, tells or implies a story".
