I'm going to treat this as a dialogue rather than an argument, if possible. Yes, this conversation has been held before in other manifestations. I don't intend to "win" anything, I just am going to throw out some thoughts to chew on.
WARNING: Wall of text, incoming [As is popular to say these days]I played Rondo last night: the pirate ship level, level 1, level 2', and the swamp. I wanted a quick Castlevania play and I wanted to see if I've judged the game wrong. Unfortunately, I came up with that same disappointment, wanting to love it and have a lot of fun with its scope, but coming up feeling somehow bored. First thing I noticed was there is a good deal of one-on-one, like a fighter, like Sinful said. For the first time, I realized one of my issues with Rondo--it has some of that halt-the-pace "arena fighting" that the post-N64 3D Castlevanias are so fond of. Rather than having a lot of traps and death pits in a forward-moving, thinking-on-your-feet rhythm, you end up walking into a corridor/room, stopping, and going one-on-one; and often, the AI isn't even interesting enough to warrant it. You can kind of muscle your way through. Now, level specific...
Level 1: To be frank, you walk forward a short distance, go up a one-screen staircase, walk forward a short distance, go down a one-screen staircase. During this, you will run into, what, 5 bone apes that are sitting ducks, and two skeleton ninja-types who don't offer much more in their environment. From here, you can choose to go forward and go on a one-one-one fighter battle with golems in what is essentially a long, repeating corridor. Or, you can go left to the secret passage. That secret passage, after one poltergeist, drops you down into a basement (?) that lets you choose left or right. Given stage progression, it's pretty obvious to go right; but if you go left, you can have a pointless battle with a plant. And the statues, who point which way to go, have a nice laugh at you. That's pretty random, and not much of a punishment if it was supposed to be. Meanwhile, you go right, and the stage is over. You're suddenly on a water-bucket ride to the boss. Maybe that basement was an underground aqueduct? The level is short and essentially disposable, even for an intro stage, and the short cut makes it even shorter and easier.
The whole idea of the first official level having a split path seems confused game design, as they've given you a choice before they've even established a rhythm to the core level design. The intro cut-scene level where you have a chat with Death already established whipping and jumping to an extent, but a linear chariot doesn't exactly set up the core level design of the game, before it can introduce its multi-path hook. So, rather than a complete surprise, the option of an extra path, which is easy enough to stumble upon, becomes less significant as a change-up/curve ball. The stage design of Dracula XX takes more advantage of showing you the ropes while not holding you by the hand, establishing a core rhythm. And, it takes advantage of the brilliant setting originally presented in Rondo, by having you interact with more burned-out buildings and structures. It feels like this town has been totally besieged. Again with the core design, the enemies take full advantage of their environment to try to knock you in precarious spots, making you think fast and ahead to strategically survive.
Level 2': This has been one of my favorite stages in the past (daylight near Drac's entrance!), but I noticed a few things when I step back. First, we have air-floating candles. Rondo is not guiltless! (As for those Dracula XX pillars in the cave--I thought it was a creative (if convenient) atmosphere where Dracula's Castle has its foundations build into the earth…or maybe it’s part of an ancient ruin site. It plays with the imagination). Anyway, once again, the split path comes very early, and it's almost forced upon you when the floor breaks if you're not paying attention, because it has you eying your enemy so much in a one-on-one battle.
It hit me that this stage may have been the inspiration for the infamous stage 3 of Dracula XX with the medusa pillars. Here's why that is better, IMO, though. Here, when you fall, if you die on the moat ride, you return to before you fell, erasing the consequence of your inexperience. In Dracula XX, the consequence is you fail to save the girls, and you have to fight Annette herself on the clock tower. You have the curiosity to continue forward, and then later realize your mistake and start again on a new code or with a password. And speaking of the medusa pillars, as tricky as they are, they feel both more fair and more interesting of a problem to solve to me in their patterns than the merman that start popping up in droves, and you basically have to stay on the front of the boat and whip quickly, and hope they don't get you in a chain of knockbacks. Both scenarios can be considered cheap, but to not acknowledge they are of the same basic ilk would be unfair.
By the way, speaking of consequences, the reward for surviving the medusa heads gives you a chance to rescue both girls by holding onto that key, which allows you to succeed in the game in one true path you work to discover and overcome.
Swamp level: Like I said before, I don't like the abrupt ending of the Dogether path, even though it's a fascinating gameplay mechanic in theory. And what's with the mid-boss on, like, the second screen of the level, and the secret passage before that, which gives you the power to annihilate it. It makes a pretty sight, but even without the secret bonus equipment, this purple skull thing goes down way too easily.
Pirate ship/ghost ship: The introduction is classic in nature, but seems a bit off somehow in the way you can muscle through it. The skull heads from the water are neat, but don't match the motif as well as the water skulls used in XX's Sunken Temple, which were put instead in Rondo's Clocktower to, IMO, lesser effect. This level's shortcut doesn't give you much difference, except a chance at an extra life by whacking what appears to be a mechanical engine(?!) That seems out of place and very quirky--more than needed. The duels with the skeleton archers and such a just little tired—padding-like. And then we get that "cheap, cheap, cheap" painting enemy. Really funny, ripping me up like that. An item crash has something to say about that. The whole thing doesn't seem fair either way to me. That part irks me.
Dracula XX may not have all the enemies or bosses of Rondo, but it does have some new ones of its own that are pretty nice. The Cerberus is a nice change-up for an opening boss; the underground swamp cave Necromancer is totally cool with its ability to slow you down, summon skeletons, and toss graves around (or use them as shields); and the tragic Annette boss is more involved than Rondo's Carmilla with its mobile magic eyes, and even inspired a turn of events for the PSP revision of Rondo.
Now, Sinful, as far as Adventure Rebirth and the Nintendo 64 games...
Adventure Rebirth has probably been the only recent Castlevania game that really lived up to the name (as I see it) and made me hopeful for the series. That said, while it does a lot with what little resources were likely allocated toward it, and is very clever in its own right, it's not necessarily as impactful as its 16-bit brethren. You can play it whenever you want, but I don't know that there's a rush, considering it was the last Classicvania-style game released. As I said, I think the game's genius really shows in Hard Mode--where it is really a struggle for survival the way the enemies are placed and the obstacles are designed, and you have to use every resource available
(such as keys, secret passages, extra lives, and sub-weapons)
--whereas the other modes are just average, maybe even casual CV romps. (Thanks for the Gradius history lesson. I wasn't aware of that, as I have only casually followed that Konami series for some reason).
The
Nintendo 64 games are basically a case of games that came around at the wrong time. People wanted SotN on N64, or a 3D equivalent. The Nintendo 64 games are instead a 3D blend of Castlevania IV and II with late 90's survival horror-ish and/or Tomb Raider-ish elements. (And given that those latter two have things in common with Castlevanias of the past, it's a clever mix to move the series forward while still being true to it). It's especially nice that these are the only two 3D Castlevanias that don't rely on the fixed camera, hack-n-slash arena fighter formula for primary level design.
Castlevania 64 or CV64 (just called Castlevania on the box) was first, followed shortly after by Castlevania: Legacy of Darkness (LoD). Basically, the creators (no longer major forces behind Castlevania these days) had a big vision--bigger than either of these games based on interviews and beta versions. However, the time crunch caught them. CV64 was a complete game, but only roughly half of what their vision was actually made it into the product. So, through one means or another, they were allowed a few more months after CV64 was released to continue working on the game--for a revised expansion of CV64, if you will. Even then, the final result was seemingly only maybe 85-90% of what they wanted based those on earlier interviews/betas (swinging across gaps like IV and Bloodlines, shown in a pilot-promo video, was still left on the cutting room floor, for example, even though some of the latches to connect to were left "visually" in the game on some areas).
The released results, however, remain rather compelling despite being a bit rough around the edges, and each gives a distinctive, engaging experience dripping with CV “mood.” I haven't played LoD since it came out and I beat its first character's quest on a rental, but I still own and play CV64, so I'm going to give you a limited assessment partially from memory and recent research. I'll just spell out the basic contrasts of these games, similar to what you'd find on the back of a box, but not give away specific spoilers. (BTW, I still plan to track down a copy of LoD in the future, unless it’s released in some sort of collection or as an official download).
Now, CV64 and LoD share some levels, but like Rondo and Dracula XX, they have completely different layouts, goals, and/or enemies/bosses. For those levels they share, the differences become a personal preference, as the freshness of the alterations are welcome, but the differences often make you miss one game's level layout or the other. On the other hand, each game, depending on the character you use, gives you new levels/routes with totally unique themes/locations. That gives it a bit of a CVIII feel at times. (So, in essence, this variety makes you want to play both games for the full experience. LoD is more than a simple remake of CV64, and vice-versa).
Other differences include the cast of characters [and their outfits] and the story. CV64 has 2 characters, LoD has 4. LoD's main [starter] werewolf-ish character serves as a prequel chapter to the story of CV64, and manages to fit well into the CV world. LoD worked to hone the camera a bit more, and it added more power-ups and such for game balance--it skews the game a bit easier, though, IIRC.
As you noted, the main whip character, a personal favorite, has to be unlocked in LoD, whereas you can choose him from the start in CV64. It's my opinion that CV64 should be played first; although, keep in mind that it's a little rougher around the edges than LoD. I think you'd like CV64 to start with given your tastes here so far, as it's a little harder, it has a whip character to start with, and some of its levels are superior to their remade versions in terms of old-school philosophy. ***Level 2 of CV64 is a near-perfect translation of 2D Classicvania in 3D, which no other game post-N64 era has gotten close to, IMO.*** It's followed up by a 3rd level that is a fan favorite, showing off the potential for growth/depth for CV in 3D.
Honestly, these games were way ahead of their time (if I gave my list of "why," it'd have some spoilers, so I won't). But maybe they were a bit too ambitious for their platform. I don't know that they're better than the best of the 2D games, but they show the amazing potential that Castlevania in 3D could possibly equal or surpass those if built from these games as a starting point. Unfortunately, because they have such a controversial history, Konami has all but buried them, and each of the succeeding 3D games tried to build off of other combo-based formulas like Devil May Cry and God of War to far more mixed, and dare I say, series-compromising results.
The reason I'm not around here much is that the recent turn of events in the series has pretty much alienated me, and the lack of good news upsets me. The series ultimately hit a dead end with the repetitive Castleroids (some of which were better than others and deserve some credit), and then the 3D series was so mismanaged post-N64 that it ended in a reboot, Lords of Shadow, that re-imagines Castlevania so much, and uses 3D in such an amorphous, trend-heavy way, that it's like the series doesn't believe in itself anymore. It’s like it feels it has to keep the barest surface elements and largely follow popular design trends to be like other popular games to make Castlevania relevant. Mixing games like God of War, Shadow of the Colossus, Uncharted, and movies like Lord of the Rings, Van Helsing, and Underworld doesn’t add up to Castlevania, IMO.
In general summation: CV64 and LoD=huge strides in right direction; PS2 Lament of Innocence = one step forward, three steps backward; PS2/XBOX Curse of Darkness equals one step forward, one step to the side, and three steps backward; Wii's Judgment equals three steps to the side; PS3/XBOX360 Lords of Shadow equals one step forward, three steps to the side, three steps backward. Any improvements in the recent 3D games always seem to come at the cost of the series' identity and/or gameplay; it's just sad to me. And because it sold decently, Lords of Shadow is the series’ near-future identity now.

(Maybe they'll totally rework the sequel's art direction, gameplay, level design, and story...but I doubt it'll be able to change significantly enough. I bought LoS at full price, even though I had very, very shaky feelings about it, and while amusing in its own right, it confirmed my greatest fears for the franchise).
Right now, in the least, I'm hoping that Bloodlines, Dracula XX, and the two N64 games come to Wii Virtual Console (along with Contra: Hard Corps, since we mentioned Contra). But even all of that is questionable.
PS: Sinful, which Castlevanias have you played?
PPS: Yeah, I have "no respect." Ha-ha! I just realized what you meant by that a page back. (This Respect Option--however it works--is new since I was last really active here. But, hey, anybody who gives XX any credit over Rondo isn't going to be super popular). Regardless, thank you.