Never played castlevania, but I can assume that it will be mediocre at best. Netflix originals have had a rather strong track record thus far, as they are not limited by any conventional television restrictions/requirements. In other words a Netflix original has complete freedom to tell whatever story they choose... however, even with that said, at the end of the day we are still talking about a video game adaptation - which have had a depressingly negative track record.
Mix the two together and you have my estimation that it will be mediocre at best.