"Alucard" is "Dracula" spelled backwards.
The Japanese version used a new kind of data technology which resulted in far greater sound quality than older Famicom games. This technology was not used in the western version.
The Japanese version used the standard NES font for text, while the western version had a new, "gothic" looking font.
In the western version only, you could enter different names and get different effects from them. These included starting with additional lives, or starting with one of the spirit helpers.
First Castlevania game to feature the "symbols" password system almost every game henceforth to use passwords has used.