The crazy thing is that these games, which were originally supposed to be one game, were originally supposed to have even MORE content. I compiled some of the history here several years back: http://castlevaniadungeon.net/forums/index.php?topic=4917.0 (http://castlevaniadungeon.net/forums/index.php?topic=4917.0)
There is no doubt in my mind that these are the best 3D Castlevania games to date. The first one is actually a more cohesive "game" experience in my mind, while the second one, with its refinements and additions, feels more like DLC overall. Despite each having flaws, the trajectory for this development team was looking really good, and both entries are memorable. I grew up around the NES Castlevania games, especially Simon's Quest and Dracula's Curse, and played a lot of SCVIV and IIRC a little of Dracula X SNES before playing Castlevania 64 and LoD, and I found that they were a logical 3D evolution to the series. They kept the player-controlled action-platforming and enemy placement that basically every other 3D Castlevania dropped--which is the CORE of Castlevania--while still including some of the questing and RPG elements from Simon's Quest and SotN; and on top of all that, they cleverly added their own twist of survival horror elements.
These games weren't really reviewed poorly back in the day, either. I just assumed the series would continue to build off of these games. By Curse of Darkness, though, it was clear to me that these games and their design elements had been buried by Konami. They've gained an unfair reputation over the years.
Here is my basic list of CV64/LoD accomplishments that made it into the final cuts of the games, which lays out how much they got right. (And keep in mind this was sort of a "first foray" into 3D with tons of limitations and a high learning curve; in the years since, the ambition and accomplishments seen below have actually, astonishingly, become less achieved by other 3D Castlevania):
*Multiple unique characters (up to four in LoD, two in CV64) with alternate levels/bosses (some even optional)
*Full 3D gameplay (ala Mario 64, so it's not "on-rails")
*Multiple endings based on performance
*Level design features spatial depth (vertical and horizontal--not flat hallways)
*Day-and-night cycles with time-sensitive events (like Simon's Quest)
*Weather effects (rain, lightning, moving clouds, and "fog"--the last one likely being a graphical shortcoming that actually helped)
*Dynamic, real-time lighting (next to candles, for instance)
*Spot-on creepy atmosphere
*Death-defying platforming of all sorts (including ledge grabbing).
*Environmental/enemy hazards (medusa heads, spikes, guillotines, buzz-saws, cannons).
*Innovative survival-horror/suspense elements
*Vampires that pretend to be human and vampires as regular enemies besides bosses
*Status changes, including poison and vampirism
*Manageable questing with inventory items (meat, keys, cards, cure ampules, etc)
*Interesting, involving plot (characters like Rosa, Vincent, Renon, Malice, Henry, etc)
*3D in-game cinemas
*Some voicing
*Unlockable alternate costumes
*Long and short-ranged attacks (IE: whip + sword), plus classic sub-weapons
*Upgradable sub-weapons (in LoD)
*There is a useful slide and duck/crawl play mechanic (that can also be mixed into custom attack combos)
*Diverse mix of old and new enemies in 3D