The color theory used in this show is quite awesome. Unlike most cartoons it uses a series of soft inter blended colors in its backgrounds similar to the old samurai Jack's artwork except instead of being sharp and pointy in order to generate a sense of other worldliness and action, everything is rounded and very inspired by 60's and 70's music albums creating a kind of nostalgic feel to everything.
As for the story, it's alright. As Miscreant mentioned it tackles allot of subject that you used to see but don't anymore, like the death of a parent, nihilism, the identity of the self, what it means when you realize your heroes may not be who you thought they were, and puts itself together rather well while still allowing for weird characters. Such as Onion the most evil and powerful being in existence.
As for the animation, it's pretty fluid, unlike most shows now days that force everything to be on model at almost all times its closer to the old animation that created scenes from your nightmares if you ever paused it, but lends itself really well to action scenes or emotional moments.
That and all of the characters are horrible people but still likable, for me at least, everyone else hates Ronaldo.