Even at $16, I have a hard time recommending Eternal Sonata. Just couldn't finish it on the 360, and I wanted to like it so much, because the story's concept was quite interesting. But the writing was very juvenile, in my opinion. I almost always finish RPGs that I start, but this was one that I gave up on.
I finished it. I'd give it a.... 70/100. The visuals were fantastic... if a little misplaced for a game with combat in it. The combat system was unique, fun, but gimmicky.
The story concept was good. But like you said, the writing was laughable. It was typical anime characters trying to sound introspective, but coming off as mentally handicapped.
The lack of visual display when changing weapons and armor was disappointing too. And I never really got the whole "playing a song with an NPC" thing.
All in all, it's a decent RPG. Overrated in my opinion, but worth a play through at 10-20 dollars.