I basically agree with shelverton's assessment. The thing is, Castlevania used to be on the heels of series like Mario and Zelda in terms of notoriety between about 1987 and 1992. However, after the success of Super Castlevania IV, there was nothing that really hit big in the consciousness of gamers until Symphony of the Night.
Essentially, the marketing/managaging of the series after SCIV was inconsistent. Castlevania had made its fame as a franchise on Nintendo home consoles, and after IV, Rondo of Blood was not only released on PC Engine, but was not even released in the US (until recently). Moreover, even though Rondo had some interesting gameplay ideas, one has to wonder what people would have thought about the loss of effects and dynamic swing controls found in SCIV.
When Castlevania finally made its way back to the US 3 years later, it was on the Genesis with Bloodlines--which split the fanbase in terms of console ownership. Then, 1995, Dracula X for the SNES arrived. (Despite being a very fun entry in my opinion), it was doomed for three reasons: It was not the infamous Rondo of Blood that some wanted, it did not have as much control or visual innovation as SCIV, and it was years removed from the release (and gamer awareness) of the last universally successful Castlevania title.
In 1997, with Sony Playstation bringing renewed interest in gaming, Symphony of the Night was released. In actuality, I don't know if this game was a well-received off the bat as SCIV, but it would go on to reignite interest in Castlevania and redefine the series for many. Again, the follow-ups would take a different route in terms of design and console with CV64 and LoD, which split the fanbase (these games were actually quite good, but people forgot that Castlevania is always trying to innovate and were hoping for a continuation of Symphony of the Night). The turning point--and curse--for Castlevania, was the release of Circle of the Moon. It was on the anticipated Nintendo GBA platform as a launch title and combined classic whip action with the style of SotN. It did pretty well; but it set an unsettling trend of also-rans. After that title, IGA took over and continued the SotN pattern with a few, random exceptions (Chronicles, Judgment). I think Lament of Innocence actually, ever-so-slightly captured imaginations that Castlevania might rise again, but the release of Curse of Darkness killed the momentum. (And stuff like Judgment, even with good intentions, has made Castlevania seem like a niche joke). The Adventure Rebirth was a nice nod to what the series is all about, but it's a drop in the bucket...and with the way gamers are used to Metroidvania now, it probably seemed weird to the mainstream modern crowd.
In the end, Lords of Shadow is in an interesting situation. It has a lot of buzz from those with a historical sense of gaming, but it doesn't appear to be on the radar of the mainstream God of War, Devil May Cry, Ninja Gaiden fans. The truth is, the name Castlevania is associated with portable Metroidvania/Sotn-nostalgia these days. Thus, the name Castlevania doesn't hold a lot of clout. I think the best outcome is Castlevania getting a revival of Ninja Gaiden's level...but that wasn't wholly true to the essence of Ninja Gaiden and also has never risen Ninja Gaiden to the heights of the top series. I'm concerned that the desire to make LoS more mainstream has crippled its ability to stand out from the crowd and capture any of the top spots in gaming.
(As an aside, you mentioned Metroid as a successful franchise, but that's a more recent trend. While the first 3 did well, the series was all but forgotten until the success of Metroid Prime. Since then, it's been more visible, but is still fighting to find its modern voice).