I really do have a hard time sorting out which classic Castlevania comes first on my list. Bloodlines usually ends up down that list, but I still like it a lot. They've all got very good things about them, and things I don't like. I think, for the most "pure" experience, there's really no other way to roll than the original. Although one could do a solo run of Castlevania III as well (I have!).
I mean, in my head, almost all of them are neck-and-neck, and depending on how I feel, that order is going to change. Bloodlines goes above the SNES Dracula X just because it feels more fair, but I love how Dracula X plays. They both go slightly below the other main games, but the fact that Konami maintained a good amount of consistency between entries is certainly laudable.
You know, I don't know where I'd put Simon's Quest in all this. For the longest time, it was my favorite. I think, if you catch me on the right day, I'd still say it is.
