This game just came out not to long ago and I haven't actually had the chance to play it myself yet; since I don't own an Xbox360; but I've been following it ever since I found out about it.
The character designs are just beautiful and I'm hoping to cosplay as one soon, though I'm not sure who yet. I'm thinking Allegreto, Beat, Polka, Chopin, Salsa, or Jazz at the moment but we'll see how that narrows down XD; (I have way too many things I want to do..)
I've only managed to find one Eternal Sonata cosplay on this site so far and I'm hoping to see more within the next few months
Because, come on! When else do you get the chance to cosplay as a famous composer?!
If you want to know more about it, check out the entusiasts community
and be sure to register (because not only do I get some points for it, but the people in the community are uber nice). Or there's always the official site