Castlevania: Chorus of Mysteries
This is a ROM hack made from the original Castlevania on the NES. This is, in my opinion, the most thorough and best hack I have seen for Castlevania. The entire game is remapped, monsters, stages, color palettes, even the entire soundtrack. Some people argue that this game can be a bit too hard at times, but a good Castlevania game should be a challenge.