Have you seen the previews for Castlevania: Dracula X Chronicles for the PSP? Its a 2D side scroller in a 3D environment similar to Mega Man Network Transmissions for the GameCube. It looks good, but it could look better. Super Paper Mario is a very good starting point for an awesome looking Castlevania game.
Take the characters/enemies and make them flat anime style artwork (much in the same way as Super Paper Mario characters are… well, the artwork part being flat not the anime). By doing this the camera will be able to zoom in and out and the characters/enemies will retain their look without pixilation or distortion. The backgrounds should still be 3D for easier level design and depth… Gears of War shows just how beautiful backgrounds can be. Since the backgrounds are 3D, it should be a lot easier to layout the levels and it turn their size should be considerably smaller. What does that mean? Means you could easily make a game twice the size of Symphony of the Night in less the time. Add some anime cut scenes, good voice work and ability to replay as another character and you’ve got a formula for title to rival Symphony of the Night as the best Castlevania game.
Actually, how cool would it be if after you finished the game you came behind the already beaten castle as a different character? The traps and switches are already triggered and environmental changes have already occurred, but now a new presence has disturbed the place. This means new enemies and bosses and the designers could totally destroy existing areas to create new ones. Imagine a long hallway in the first run through is tore wide open by some colossal creature in the second run. Turning it from a corridor into an open area where the battle takes place in what remains of a hallway, its roof and whatever hangs in the sky above it. The possibilities are endless.