This is easily the best of the three GBA Castlevania games. New to this game is the soul-fusion system. Every enemy in the game has a soul which you can steal. Once you steal their soul, you can use their powers in some neat fashion. For example, steal a skeleton's soul and you gain the ability to throw bones. Steal a manitore's soul and you can grow a scorpion tail which you can use to attack enemies.
This game is a very fulfilling experience and is one of the best games available for the GBA.