Castlevania's introductory scene is nearly identical to the one found in Vampire Killer, with some minor changes in Simon Belmont's color palette, which changes from a dark red to a golden brown. The proceeding scene lets you take control of Simon in a small courtyard area, where you collect an initial set of items by whipping a series of torches that eventually leads to the massive doors of Dracula's castle. From that point on, Konami obviously wanted to take a different approach from the one it used with Vampire Killer because Castlevania's gameplay deviated from Vampire Killer's nonlinear structure. Instead of having single-section rooms with multiple exits, Castlevania features long scrolling hallways, where there is usually only one way in and one way out, with a few hidden rooms in between. Plus, none of these entrances or exits require any sort of key. Konami wanted to keep up with what was popular for consoles at the time by producing a straightforward platformer, but who knows what might have happened to the series if the company simply did a port of Vampire Killer for the NES.

Though Castlevania is different from Vampire Killer, it should also receive credit for introducing conventions that were reused in later games. Shopkeepers in Castlevania are nonexistent, so hearts are now used to power Simon's special weapons, which include holy water, the holy cross, axes, daggers, and the stopwatch. Different items, like the stopwatch--which uses five hearts instead of just one--also use a varying number of hearts, so your inventory of hearts can deplete quickly if you aren't careful. Castlevania also introduced item power-ups like the Roman numeral items, which let you throw either two or three special weapons in succession rather than just once.

Other than a few basic gameplay mechanics, Castlevania for the NES started another important trend in the series--music quality. From the upbeat opening track--appropriately named Vampire Killer--played in the first level of the game to the maniacal boss fight theme, Castlevania's soundtrack is incredibly dynamic, and it comes as no surprise that many of its songs were remixed and made even better for future games in the series.

After the widespread success of Castlevania, Konami had a new franchise on its hands, and it quickly went to work on a sequel to Castlevania. However, when the game was finally released, many fans were left scratching their heads and wondering if it was a true sequel to Castlevania.