Castlevania: Dracula X
While Japan received Castlevania Dracula X: Rondo of Blood, fans in the United States had to wait two years to see Richter Belmont's first adventure, although the form we got it in was, arguably, quite flawed. Structurally similar to its Japanese counterpart, featuring Richter Belmont once again on his way to Castle Dracula, Castlevania: Dracula X (referenced most often as Dracula XX based on the Japanese name for the game, Akumajo Dracula XX, translated as "Demon Castle Dracula Double X", and titled Castlevania: Vampire's Kiss in Europe) is a drastic re-imagining of the original game.
The reason for the SNES port is because NEC of America, the controlling interest of the TurboGraphix 16, had a limited view of what games would interest American audiences. A number of fun titles for the Japanese version of the console, the PC Engine, were never ported over to the U.S. (and other markets) due to the disinterest of the American group. They felt that Americans were only interested in shooters and basic RPGs so other titles that did well in Japanese markets, such as Rondo of Blood, were rejected.
Owing to the limitations of the hardware, much of the PC Engine game had to be scaled back for the SNES. This led to different music (that had to come from the SNES sound board instead of off the higher quality CD audio of the original), different stages, and a remixed overall experience. The biggest change, and the one most people point to as Dracula XX's greatest flaw, is the fact that Maria Renard was not a playable character in this game. Although both games featured characters for Richter to find throughout his adventure (four in the original, two in Dracula XX), Maria only serves to give the players the best ending in Dracula XX; otherwise, unlocking her has little bearing on the game.
Interestingly to note, though, is that the game did have one lasting difference for Maria: in Dracula XX it was established that Maria Renard was the sister of Annette, Richter's betrothed). Maria being related to Annette was implied in dialogue in the sequel to Rondo of Blood, Castlevania: Symphony of the Night, with Maria being Richter's sister-in-law, and this is the game that established that tie, even though all the producers on the later games have said she's not related to Annette (despite the dialogue in the games saying otherwise).
While the plot and basics of the game are largely the same, Dracula XX diverges greatly from Rondo of Blood in levels and level-design. Some levels are close stylistically (such as the two very different "Village Ruins"), but the order of many has been changed, and some stages are swapped out completely (Dracula XX sports the "Sunken City" instead of the "Haunted Ship" or "Docks"). All the levels are completely different in layout, including Dracula's "Castle Keep", which now doesn't even have the traditional staircase up, and features an end-room of tiny columns instead of the standard throne room (making that boss fight drastically harder).
And that points to another fan-commented "flaw": the game is substantially harder than it's PC Engine predecessor. Monsters are positioned in hard to reach places but still can easily tag the player, and everything in the game is structured to make the game unbearably difficult to play. While most Castlevania games are hard, Dracula XX wasn't viewed as unfair. Actually bothering to make it through the game at all is considered an accomplishment by some within the Castlevania community.
All the flaws combine to make a game that not only sold poorly (churning a dismal 90,000 units over the course of its life) but was eventually replaced in continuity by its far superior original version. Even the designers of the SNES port considered the game to be a side-story/alternate-continuity retelling of Rondo of Blood and not a proper replacement for the original title. This led to the official compendium of all things "Dracula X", Castlevania: The Dracula X: Chronicles, excluding the SNES Dracula XX from the collection. As far as Konami is concerned, this game is better left forgotten altogether.