No they nearly always completely ignore the original story line. Look at Resident Evil, it's a complete crock. Expanding a game plot is not hard, they are just retards. Breaking it down into 20 minute or half hour segments is damn simple. Their best idea of Castlevania is a horrible mess if script outlines are to be believed.
Castlevania in easy 30 minute steps without fucking it up:
Note - this would need multiple characters for a script to work, have Trevor and his companions for example. This would also allow development such as Alucard's inner demons, someone for Trevor to express his trouble over the family's repeating destiny.
Act 1: Character setup - The Belmonts (action beat: some monster killing, love interest gets kidnapped)
Act 2: Draculas Castle - atmosphere and mood setup (action beat: simple enemy battles, skeletons etc. Half way point - cliffhanger)
Act 3: Inner castle - caves / laboratory / clock tower exploration (action beat: death trap escape, larger character battle)
Act 4: Kickass finale - But enough talk have at you! (epic scene and some fan service, a badass D transformation everyone wins)
Alternate plots that could be expanded - the Soma Cruz storyline, Richter and Maria, Leon and Mathias. It's not hard, filmakers are just idiots.