The 3D castlevania games are more of a nod to games like god of war then true purist old school castlevania games. I played through that game to completion and its a fun game. There are some short comings but as far as on its own merits its definitely worth playing.
When it comes to castlevania there are three styles of it. LoS is a example of a 3D castlevania game. And is like just as I described above.
Then there is what gamers call metroidvania. This is a 2D style of castlevania with backtracking and exploration and finding secrets and so forth. Often you need new powers or abilities to be able to get to certain areas and the games lock you out of them til you are ready.
Oldest is traditional level based Castlevania, which has you going through levels from beginning to end to reach the end. This is the hardest type of castlevania game and is most unforgiving.
So there is no real one way to get into the series, I suggest sampling from all styles and seeing what fits you.