I never played the original Castlevania on its original platform in its original era. I only got around to it when they released it on GBA. So I think my opinion's unclouded by nostalgia when I say that, with reservations but in general, I like it.
In the pantheon of retro classics, Castlevania slots in right next to Ninja Gaiden. Both are sidescrollers emphasizing close combat (as opposed to Mario-style hopping), with health bars and a rudimentary power-up system. Castlevania has better secondary weapons. Ninja Gaiden has better level design, and is probably the superior title overall--the flow of its levels is pure 8-bit choreography. Either way, they're simple games. Over the years, Ninja Gaiden has stayed fairly simple. Castlevania has not.
Which brings us to Order of Ecclesia, the most recent side-scrolling title in the series. It's not that OoE is a bad game, so much as it is way more complicated than it needs to be.
I'm giving up on the game about seven levels in, having gotten through the first four bosses or so. I'm doing so because the level design (which is awful, having largely abandoned the intricate "Metroid-vania" style of navigation) has begun throwing in enemies that completely wreck the difficulty curve (specifically, the demonic gravediggers). The options available seem to be either learning an attack pattern that's not particularly enjoyable, or improving my character. Since neither appeals, I'm ditching it.
"Improving my character"--what a fun turn of phrase that is, as if Castlevania were Emily Post and Buddhism mixed together. What it really means is going out and either leveling-up (a long, painful process left over from RPGs that I thought we had largely abandoned in the civilized world) or tediously killing the same enemies over and over again until they drop a more powerful weapon. It's all the worst parts of World of Warcraft, but without a sense of humor!
This complication doesn't have any particular justification for its existence. Its only point is to add a pseudo-cerebral tint to an otherwise fluffy and unredeemable arcade experience, something it has in common with the vapid plots that Konami insists on jamming in there, as if I really cared. "We're not just engaging your reflexes," OoE defensively protests, "we're engaging your mind!" Yeah: because making me constantly interrupt play to struggle through a poorly-designed menu system, all to find the collectible weapon that will harm this particular recycled sprite from the last seven Castlevania titles is certainly a challenge that will stretch my capacity for non-linear thinking, isn't it? Give me a break. These games are basically mental Diet Coke. The least they could do is have the dignity to act like it.
Let's make a deal, video games: you don't make me grind for a frakking sidescroller, and I won't sell you on eBay.