Making it better, IMO, would result in what I've dubbed "Castlevania: Curse of Darknes - The Vampire Killer Cut". Here's what it would include:
- Most areas are cut into two separate areas(Mortvia Aquaduct and Temple become two different stages, with the tower to the Skeleton Diver appearining at the end of the aquaduct, and a new boss apearing in the templ). Larger areas will contain multiple stages(particularly the Abandoned Castle and Dracula's Castle).
- Stage/area layout is far more platform friendly and features overall better level design(no "every path in the Forest of Jigramunt looks the same" BS). Each area would be chocked full of variety(Eneomaos Machine Tower would actually resemble a real clock tower that CV a 3D CV could be proud of). An example, using Jigramunt, is that your trek through that stage would lead you venturing into the forest, through a brook, near perilous strctures(like those buildings in the Mad Forest), graveyard of statues(nod to the place you rescue Sypha from the Cyclops), over the marshlands on a ruined bridge(nod to CV2) and up into the treetops to cross to the other side where you fight the forest's boss, THEN you go to the cave(which is it's own large area of cool tunnels, forgotten catacombs with Alucard's coffin easter egg, and a subterranean coliseum leading to the Minotaur battle). There should be nods to familiar locations in CV3(like I said with the Mad Forest nods). What the Abandoned Castle did with CV1's castle, the majority of CoD's locations should've done with CV3's world.
- All characters from the original CV3 make an appearance(some, like Alucard, a cameo). Grant and Sypha SHOULD'VE appeared, and been tied deeper to the story. Cordova should've been an interesting story point, where you enter the town and people are sounding a bell(in Silent Hill fashion), running for the houses and locking up as monsters start pouring in. There you'd meet Grant and aid him in taking out the monsters, splitting up to find the source(which of course, is Isaac at the ruined church courtyard). They should've also had flashbacks to the events of CV3, showing what exactly they were all doing at the time, how Hector and Isaac managed to leave before Trevor and crew stormed the castle, Alucard's familiarity with the Devil Forgemasters and Hector's past which was explained int he comic(and SHOULD'VE appeared in the actual game via cutscene). Add a little more umph to the world, everything was so dead. Garibaldi Temple, show it being inhabited by evil monks who have pledged allegiance to Dracula and are lead by none other than Zead/Death.
- More explained story points. Explain why the Abandoned Castle resembled the castle from CV1, and why Dracula's Castle looked nothing like any Dracula Castle in any CV games before or since. Explain the significance between the Belmonts and the Infinite Corridor, why the entrance was in the Abandoned Castle's keep, why it takes a Belmont's blood to open it, and, well, everything about it.
- For each new area, add a boss. Mortvia Aquaduct and Temple would have two different bosses. Garibaldi Temple and Monestary would have two different bosses. Forest of Jigramunt and Cave would have to different bosses. Dracula's Castle, in particular, will have many bosses other than Death, Isaac and Dracula. Some old classics could return(Phantom Bat, Mummies, Frankenstein's Monster). My personal idea, interestingly enough, was that the final boss was NOT going to be Dracula. Dracula IS fought, defeated, but when Hector attempts to forge Dracula's curse into something else, he gives it a physical form, a sort of dark chaotic energy(like DoS's Menace) and battles it. This creature is the red beast seen in that infamous Kojima poster(the apocalyptic beast).
- Trevor mode is it's own unique game with it's own story(that takes place during Hector's adventure). You see the story through Trevor's eyes, and venture around Wallachia trying to discover why Dracula's Curse remains after Dracula's defeat years ago. In the normal game, you encounter Trevor, and sometimes fight him as a boss. In Trevor mode, you play the otherside, and encounter Hector, sometimes fighting him as a boss. Other than that, some of Trevor's bosses differ than Hector(Trevor might fight some more familiar CV bosses, like Bone Dragon King and Leviathan, in place of some of the bosses Hector fights).
- Personally, even though it wasn't known at the time, i'd like to see a hint at the future descendants of Hector and Julia being intertwined with the Belmonts centuries later(perhaps Shanoa is a distant descendant).