Art: Main thing. The art quality overall is ultra impressive. Animation is just the best I have ever seen. On fights they push animation fundamentals to the limit, very well executed. I don't think I need to say much else.
Sound: Cool music, and very suitable and detailed sound effect for all little things. And very good use of sounds, giving impact to the action scenes.
Character: There are a lot of superheroes, everyone with a well defined role and uniqueness, fitting very well with their appearance.
Enjoyment: Certainly on my top 5 most enjoyed animes. For the first time on a shounnen I have seen fights dense enough to satisfy me. Less talking, less smoke fading out, faster actions. There is talking and padding out in the middle of fights, but in most cases the action sequences last at least 5 seconds. The fight on the last episode was really amazing. They have put a lot of work on the actions scenes and its really appreciable.
If you like to see action and fights amazingly animated, this is a must.
