In my opinion the hardest game was castlevania dracula x for the snes. the final battle with dracula on the pillars.
Wait, what? That whole game and final battle are easy as pie. Just use the ax to fight Dracula.
I love
Dracula X for SNES, by the way. Not near as cool as
Rondo, but still neato. I love the graphics. Reminds me of a more cartoony/colorful, less dark
Demon's Crest.
Bloodlines I don't find difficult either, although the limited continues is kind of a pain.
As far as classic
Castlevania games go (not including
Haunted Castle, since arcade games are always tough to mine you of quarters), the X68000 game is probably the most difficult, in my mind. Well, not overall (it's pretty easy), but some of the later stages are a bitch. More specifically, I have the hardest damn time with the clock tower and its boss. But I'm sure there's someone reading this who can breeze through that stage.