When the Castlevania series is talked about, it's always discussed in terms of "old" and "new", "classic" games versus the more modern Metroidvania titles (which, if you know anything about Metroid and Castlevania II, isn't any more modern than the old-school games in the series). Fans talk about these games like there is a clear deliniation between old and new, a point in time (Symphony of the Night) when the series became the modern franchise we know.
Looking at the actual release dates of the series, though, this clearly wasn't the case. The first game to come out after Symphony wasn't another Metroidvania game but a little, classic-style platformer on the Game Boy, a far cry from the Playstation home of the previous game.
Set up to depict the earliest Belmont encounter with Dracula (presumably because much earlier and Dracula wouldn't have been born yet), Castlevania: Legends follows Sonia Belmont, progenator of the clan and the first female Belmont in series history. Along the way in her journey, Sonia would meet up with Alucard (giving this game some semblance of a connection to the previous hit title), getting advice from the vampire's son. She'd then end up collecting special items and taking on Dracula in a rather plot-heavy little Game Boy game. It's just a pity that Sonia's game wasn't very good.
While the story of Legends was all well and good -- and admirable effort to explain the origins of the clan while at the same time striking a blow for equality in the vampire hunting workplace -- the game wasn't all the fun to play. Muddy graphics, slow mechanics, and cruel level design hampered the game more than it should have. Considering that the last Game Boy Castlevania games had come out years earlier, Konami should have been able to do a better job with the lessoned they'd learned in the interim.
Instead, Legends ends up being a sad final note on the classic game play of old. After this, Castlevania for the Nintendo 64 would try to update the classic gameplay for 3D consoles (also to muddy effect and little fanfare). The failure of that game would prompt Konami to all but abandon the classic series entirely, moving forward with Metroidvania games and the Lords of Shadow reboot series.
As a sad final note, Sonia was later removed from the official continuity, all but ensuring her as but a footnote in the grand series history. He role as progenator of the series was taken over by Leon Belmont (in Lament of Innocence), her next game (Castlevania Resurrection) would get cancelled, and Sonia was left on the sidelines.