Play it for the awesome soundtrack and the dating-sim aspects, not so much as a RPG
Just like the Atelier Iris series, Ar tonelico is an old-school type of RGP. The character designs and town background images are aesthetically pleasing, and sometimes breathtaking, but in dungeons and battles are where the graphics feel outdated. It's not necessarily a bad thing, but it certainly leaves something to be desired.
Other than the familiar item crafting system, this game has a very heavy dating-sim element, where the main character can (oh my) "dive" into 3 different girls, and explore their inner thoughts. Who you choose to be with will alter the ending that you get.
During battles, you have 3 melee characters and one of 3 girls who can cast magic. The goal is to have the girl in the back charge up her magic while the other 3 pound enemies/protect her if she being targeted. Sounds interesting, but in reality everything is so easy, casting the spell is not really necessary. Even in boss battles, casting spells would speed things up, but it kind of feels pointless since you'll have no trouble otherwise anyway.
To sum it up, this game is a not very good example of a RPG, but it holds together well thanks to the music and the overall atmosphere. But I have to admit, I enjoyed trying to improve the relationship with the girls more than any other aspects of the game. Not too bad of a game, you can certainly do worse than this.