Aria Of Sorrow is definitely a good game worth getting. The graphics are really good with lots of animation and sprite rotations, the soul system gives you a large variety of abilities and attacks, and the story is actually interesting and imaginative.
However, after spending two months assembling a screenshot map of the whole castle (to be published on the net probably next week), I realized that my opinion of it had changed a bit. On average, all of the areas have good graphics and layout but very few of them really stand out. While Harmony has tons of featureless corridors and some very dull-looking areas like the Luminous Caverns, it also managed to have the excellent Sky Walkway and more interactions with the castle itself like the giant Ball puzzle in the Clock Tower or pushing big suits of armor to be crushed in giant gears/clear a giant rock.
But I'm really nitpicking because in general, I had more fun with Aria Of Sorrow. It just can't come close to the greatness of Symphony Of The Night, but very few of the Castletroids do.