Animated would definitely be the way to go. Yoshiaki Kawajiri would be my top pick for production director at least in charge the first season which would of course be focused on the beginning of the Belmont's struggle against the man who would become the lord of darkness. i.e. Lament of Innocence. A full season of episodes could finally flesh out characters like Sarah Tarantoul, Mathias Cronqvist, hell maybe even Joachim. With Kawajiri spearheading the project, at the very least the mood and atmosphere of the games will be realized beautifully. Not to mention the drama between the characters would be expertly handled and also balanced out nicely with the action setpieces.
The first season would be a lead-in to follow up series, each taken up by a selection of other directors and production houses. But I would definitely say let Kawajiri return to helm both Curse of Darkness and Symphony of the Night. I would even go so far as to make the two stand-alone anime films released between their various interlinking story arcs in the series. For example, have an epic CV III season to lead into the Curse movie, and likewise a Dracula X season to lead into Symphony. Hell, keep the seasons up with enough enthusiasm from both fans and anime studios, we might even see some truly worthy gaiden adaptations of Circle of the Moon, Legacy of Darkness, Order of Ecclesia maybe a proper vehicle for Sonia to finally make her voice heard. I would draw the line at the 1999 battle though... Whether it was done or not, be it the final end-all season or a movie, I'd still opt for the door to be left open to the future of Castlevania and not touch the Sorrow titles.
....Although, if they had to be done, I would say package them as a 2-in-1 DVD movie, maybe with a third part added to show the final tragic outcome in the struggle to contain the spirit of the dark lord within Soma Cruz.
At any rate, those are my thoughts on the subject. Apart from that, refrain from cheesy or overly dramatic dialogue and keep any romantic subplots between existing characters to a minimum. Include recognizable monsters, locations, weapons, abilities, and evil servants from the games and pay tribute to the more recognizable themes from CV's rich musical catalogue. And if dubbing must be done, please let either Sony or ADV handle the English voice casting. - At least get some unknowns who put some serious effort into their roles, will ya'?