I haven't ever played it before
You seriously should, but download it off Nintendo's 3DS eShop or Wii VC if you don't have an NES to play it on. It's always the best thing to play the very first game in a very long series, just to get a better feel for its history--and Castlevania has quite a bit of that!
If you haven't played any of the NES trilogy, I suggest playing all of them. Castlevania 3 is my most favorite of them all (In fact, my most favorite game in the entire 20+ years long legacy), so I recommend that with a highest honor.