Castlevania: Harmony of Dissonance
If Castlevania: Symphony of the Night established what the Castlevania series could do, and Castlevania: Circle of the Moon showed that the formula could be repeated to great effect, Castlevania: Harmony of Dissonance (titled Castlevania Byakuya no Concerto in Japan, translated as "Castlevania: White Night Concerto" or "Castlevania: Concerto of the Midnight Sun", aka "Castlevania: White Night Concerto" or "Castlevania: Concerto of the Midnight Sun") established that, yes, this is where the series would be going for the foreseeable future. The games, as far as Konami was concerned, were going to be varying shades of the Metroidvania formula going forward. And, they were going to be overseen by Symphony producer Koji Igarashi.
As Koji Igarashi's first tile back in charge of the series (after other teams handled Castlevania: Legends, Castlevania 64, and Castlevania: Circle of the Moon), the director wanted to take the game back to what worked in Symphony of the Night. Reportedly not happy with the changes production team KCEK made to the formula (which is why Circle of the Moon was removed from continuity, at least for a time), Igarashi (who soon would take on the moniker "IGA") wanted to show how his version of the series would work on the Game Boy Advance. While this game does share having a whip-wielding hero in the lead role, this is a game that very much mirrors all the things IGA liked in his title.
Taking place in the span of years after Simon Belmont's multiple battles against Dracula (two or three depending on who you consult), Harmony of Dissonance follows the exploits of Juste Belmont, heir to the clan and grandson of Simon. When the feared, dark castle appears in the moors, Juste goes to investigate, but what he finds there could lead to one of the biggest Castlevania adventures yet. It's an adventure that will span two castles and will suck in not only Juste but his friends Lydie and Maxim Kischine as well.
Although the game takes a fair bit of inspiration from Symphony of the Night, Harmony of Dissonance does take a few nods from the previous GBA game as well. Juste plays like a hybrid of the two styles of the previous games, with his general appearance feeling more like Alucard (in style and in the blue glow that follows him), while his moves, via his whip, and magical abilities feel much more derived from Nathan Graves. And, of course, the game took one valuable bit of information from Circle of the Moon: with the Game Boy Advance lacking a back-light (at least at the time), the game's graphics had to be brighter.
Despite being a return of IGA to the franchise, as well as him placing his style of Metroidvania on the series, not everyone was impressed with the game. It was very bright (emphasis on pastel colors to appear brighter on the GBA screen), a tad confusing (with the difficulty exploring two parallel castles at once), and maybe a bit too much of the same thing as was just released in the previous adventure. Where Circle of the Moon was praised for its game play at the time, leading to sales of over a million units worldwide, Harmony barely made a fifth of that and was something of a disappointment to the Japanese home office (as per IGA's own statements). This was not the lustrous continuation of the franchise Konami wanted at the time, so IGA had to go back to the drawing board again.
In retrospect, with the distance of years since its release, Castlevania: Harmony of Dissonance is an interesting, if flawed, little title. The criticisms of the game are fair, even now, but it does also have its charms. It might not be as good of a Metroidvania as what came before (or since), but it is enjoyable enough in its own right. A fair middle title that doesn't compare as well when you look at all the awesome games to come out around it.