Ever since chapter 1, I always thought there really is something special with the art style of this manga.
From the SD, comic forms of the character to the 'serious' versions, the way the mangaka make things pop from the panels is just eye-catching to me.
Also the fact that they also ensure that proper background art is drawn tells me that this is a really high-production value manga. (there are a lot of manga out there, especially the adaptations from web/light novels where there is only crude or almost no background art)