I remember the first time I played CastleVania, it was at a classmates house and a bunch of us played alternating when one of us died. We finally reached the Count at midnight after hours of epic fails. The sense of accomplishment was incredible at the time the castle seemed huge and the boss fights were exciting and challenging enough without being cheap.
CastleVania was just one of the many Konami titles that solidified them as a leading game company. The games graphics were fantastic, the game utilized the 8 bit color pallet to the best of it's ability. Each stage was well designed with fantastic atmosphere thanks to the visuals and soundtrack, each stage had a definate distintiveness that enhanced the scope of the game, giving it the sense that the castle was labrynthian in size. Each of the six bosses felt right at home in their stage, starting with the large Vampire Bat to the Mummy, Frankenstien and the Grim Reaper. These bosses would become permanent residents of CastleVania in subsequent sequels, and the stage design would be enhanced and expanded upon in later sequels also.
Simon Belmont paved the way to become the first in a long bloodline of Vampire slayers, but he wouldn't be the first chronologically, long before George Lucas began the prequel craze in Hollywood, Konami introduced fans of the series to Trevor Belmont in CastleVania III...
Aside from the esthetics CastleVania had fantastic gameplay, Simon's primary weapon could be "powered up" for further reach and power and the effect was noticeable, CastleVania also had sub weapons scattered thruout the game, Battle Ax, Holy Water, Dagger, and Boomerang, these weapons could also be upgraded by double shot and triple shot giving Simon a virtual endless supply of weaponry.
On top of all this the boxart was amazing also!
CastleVania trully earned the Nintendo seal of quality, awesome graphics, soundtrack, gameplay, playability, boxart.