The sequel to the excellent Aria of Sorrow is by far one of the Nintendo DS's best games. It improves upon it's predecessor and takes right off from the previous plot. Soma Cruz and his soul system returns and it returns with pride and quality.
The ability to use new techniques for every creature you soul-steal was a great idea, and I loved seeing it return in Dawn of Sorrow. I spent many hours collecting all the souls I could, beating every awesome boss fight, and getting farther in the game. My favorite in the Castlevania series, and for an added bonus you can play Castlevania 3-style in a bonus mode where you can control Julius Belmont, Alucard, and Yoko Belnades. Such a masterpiece.