Soma needs to not only beat the crap out of bosses, but also seal their souls away. To do this, you must cast a spell on them. A ring comes on screen, and you must use the stylus to draw a pentagram-type shape that activates the spell. These seem a little tough to memorize, so it remains to be seen how good of an idea they are. Still, it's more dual-screen interaction, which is far from a bad thing.
Despite the fact that Castlevania has always been a single-player affair, Dawn of Sorrow features wireless multiplayer. In PvP mode, you're racing against another player -- who shows up as a ghost on your DS -- to get to the end of a maze. The rooms are full of enemies, though they differ depending on how far you are in the single-player castle. If you get extra creative, you can arrange the enemies yourself. It's pretty darn fun from what I played, and will give you and your pals a few extra hours of entertainment.
The amount of hotly anticipated DS titles is almost frightening, but Castlevania: Dawn of Sorrow sits up at the top of the heap for me. It may not advance the graphical prowess much past its predecessor, but the advancements made to support the DS' abilities brings this already-amazing series to a whole new level.