Story, graphics, music, and a great combat system. This game has it all.
The story begins with Polka, a girl who will die soon because she can use magic. She wants to make a difference in the world and travels to Forte with Fredrick Chopin, a musician who believes that the game's world is his dream. On the way they meet Algretto, Polka's love interest and arguably the hero of the game, and Beat. From there they try to explain to the Prince that the mineral water that Forte is supporting is turning the citizens into monsters. Unfortunately, the story takes a turn for the worse near the end but some intelligent people can explain it pretty well on Gamefaqs or Xbox.com boards. Music is important in most great video games but Eternal Sonata defines the importance. Since the game is based on Fredrick Chopin, a famous composer, each chapter is based on one of his works. Somewhere in each chapter they further explain the life of Chopin. Besides Chopin's great scores, the music during gameplay is simply magnificant. And you can always replay the music in one of the ingame menus. The gameplay also works really well in the RPG. Its not the standard stand in the same spot clicking one button to attack. You can move and do special attacks or regular attacks. Further on, you have the ability to do more damage with Harmony Chains which adds an interesting take especially through the second playthrough.
Overall, I'm not really an RPG fan but I found the game satisfying and worth the money.