I don't know how popular Castlevania is in GT, but I've been in the Dracula-slaying mood, so I've been playing some old Castlevania games whenever I have the chance.. mostly for nostalgia, but also because they're just so much fun.
Just finished Dracula X and Super Castlevania IV. I'm going into the GBA ones (which are my probably my favorites). Currently playing Aria of Sorrow again. Circle of the Moon is also great and under-appreciated. I'll go back to the NES games sometime soon. I did play through the first title.
Never played any of the N64 ones (heard they were kinda bleh) and I did enjoy Lament of Innocence on the PS2. The new Castlevania kinda looks like a God of War clone, but we'll see, I guess.