Just like Atelier Rorona to Atelier Totori, Atelier Meruru is a huge jump from it's previous title.
The graphic is improved (Not as big as Rorona to Totori), but the most important improvement went to the gameplay. It no longer gave you the headache Rorona/Totori had, but still quite a challenging game to complete.
Basically as the third and final Arland saga, this game is near it's perfection, learning and avoiding the faults of the previous two titles.
It's a must get if you've played through Atelier Rorona and Atelier Totori. If you haven't, that's ok… There's a prologue mode which basically guide you through what happened in the previous two games.