Going back to hack and slash type gameplay? That was only developed in LOI—a game which, for whatever reason, seems to have set the standard for Castlevania in 3D if games continue along the lines of Lords of Shadow. The old Castlevanias are just fun platformer action games that require a lot of enemy dodging and precise hitting. I'd hardly call that a hack and slash formula. (Unless you weren't referring to the classic games in that manner.)
I never get tired of the old style of gameplay because it works beautifully, and on top of that the games were designed very well. SOTN is the only SOTN-style game that I would say is truly well-made. The others are good, and pretty fun, but none are—in my opinion—exceptionally well-made games. If the games would have been a bit more fun, and not confined to the limitations of handheld systems, I might not be so tired of the "Metroidvania" format.
The Adventure ReBirth is a nice throwback to the kind of Castlevania games I enjoy most. Perhaps making those linear games fun is just a whole lot easier than making the non-linear ones enjoyable. I see no reason why more games in that style weren't being made this entire time.