Funnily, until recently i never finished a castlevania game (or played that much, barely touched the games), rondo of blood is the first i finished, and now i'm going trough the others.
Rondo of blood is freaking good because you can access different routes, which adds to the replay value.
I encourage you to play Symphony of the Night, its the BEST Castlevania of all time, its on PSX, Dreamcast, PC, PSP, PS3.
I was just playing Curse of Darkness the other day, fantastic game. Symphony of the Night is a good stop, but you might want to play Super Castlevania 4, Chronicles or Bloodlines before going into ''MetroidVania''.
is actually what i'm playing right now. i reached the upside down castle already. no guides, yay. This is not nearly as hard to find your way as it is with metroid games. And while i'm enjoying it, i still need to play a bunch to pick a favorite.
Ahh, nice. Beware of Galamoth, you'll know what I mean when you get there. You also get multiple playable characters depending on what version you're playing when you beat the game, so take a look at that.
SotN is still my favorite, with Aria of Sorrow being a close second, most of the series is amazing, sad that it also had to be an IP under Konami.