Many people seem to mistake the association that Castlevania games must always take place inside a Castle which many of the earliest games, notably Castlevania II, III, IV, Bloodlines, Rondo of Blood, and a few of the Gameboy titles, which had many outdoor areas such as caves, swamps, rivers and waterfalls, and even forests while traversing through the countryside on you your way TO the Castle, rather then simply being inside the Castle from the very beginning.
However the other thing to point out as just identifying with the series artwork style is also it's atmosphere and tone of the series. Which is usually has strong Gothic and some religious overtones. Something that is very hard to convey it in just words because I feel that is something that needs to be experienced to grasp it.
Such as when you descend into catacombs and caves, passing through dark forests and murky swamps surrounded by dark creatures such as skeletons, spectres, and demons fighting your way to through the evil as you as you approach that ever foreboding Castle passing through it's halls and that area akin to a cathedral with the windows full of paned glass, then ascending towards the upper section through the clock tower and balcony and then that final staircase to reach the tower spire to throne room with the inevitable battle against the Lord of Darkness.
That is what I feel what the essence of the Castlevania series is as was present since the very earliest games in the series, that slow build up and progression. Lords of Shadow has some of the above fairly represented giving it a place in the Castlevania series.