NSMB or Castlevania: PoR?

Hey guys. I'm looking for a great side scrolling platformer and trying to decide between NSMB and PoR. I know NSMB is one of the best DS games out, but I hear it's kinda short and easy. Which one should i get?

Castlevania just beacuse NSMB is over before you know it.

Both good games, but if you want one that lasts get POW.