Let's set the record straight. When people say that this is an NIS game, they assume that NIS made it. This is not the case.
Ar Tonelico was made by Gust, who also made the Atelier Iris games. It is published by NIS.
Now the reason I point this out is because Ar Tonelico and Atelier Iris are not quite as good as Disgaea and Phantom Brave (made by NIS). Just so there is that distinction. /NISfanboyrant
It appears that NIS is taking over some of Atlus' traditional roles of bringing over these kinds of games to the US. NIS games were originally published through Atlus until NIS was big enough to make their own American office.
But yeah, Gust/NIS is not Namco. They probably don't have (or don't want to use) the resources to produce high resolution artwork in their games, so they do seem to come out blurry when compared to 2D games of a higher budget.