Actually, I wasn't referring to other game series outside of Castlevania. I mean's between games in the series, mixing graphics across Castlevania titles, still ends up as an inconsistent mess. Too many styles have been scattered about, especially color wise. You can minimize this by rooting a true palette theme for the assets of a stage though.
Of course, making your own graphics is always best. Most people don't have the time, dedication, and in some cases money to see that through though. If you must do it at least theme the palettes together, otherwise you'll end up with something looking completely inconsistent and disorganized.
As before, the offer is extended for one free example room if you want it.