I was going to write a blog post reviewing Eternal Sonata tonight, but a) it's kinda late and b) Nathan reminded me he reviewed it 4 months ago. So instead I'm just going to link his review and add a few brief comments of my own.
In brief, this game has really pretty graphics, excellent co-op, fun battle system, and kind of awful voice acting. The plot is so-so but it's based off of Chopin's life/death, so that part's unique and cool (and also makes for awesome music). Honestly though, the game's a lot more fun on the second playthrough when you don't feel guilty skipping all the (often long and tedious) cutscenes. I really enjoyed playing it overall, and I'd highly recommend it for anyone looking for a fun JRPG game with co-op. Plus it's super cheap now; you can easily find it for $20 or less.