I think that good story should not leave out stuff that directly related to the storytelling for the viewer / gamer to use imagination. Some riddles could exist, but they shouldn't affect the immediate plot of the story, otherwise it's a bad storytelling. Definitive answers should be provided sooner or later. And if they don't - then its once again bad storytelling or bad planning. This where old canon fails hard - there is too much things that exist without any explanation or even hints. For all we know Sent-Germen could an alien-star-fish in the guise of human from another galaxy.
And imagination could only get you so far in this case, since you know that whatever you have created is non-canon and couldn't be seriously used in discussions about game story and the real answers (if ever delivered) could be completely different. I've seen cases when people confused they imagination with canon.
It's not like I encourage story to provide absolutely all answers. MGS managed too constantly keep players guessing for almost decade and they played that card very good until lately. Half Life is another example of the story, where riddles doesn't turn story into a mess, besides there is big chance that definitive answers will be provided someday. But I stand that "riddles" should be kept at minimum, answered someday and doesn't involve trivial stuff (like "Who was the son of Simon Belmont?" or "How Belmont Village in OOE came to be?").
While I agree with you, there's different circumstances with the "616 Universe" (yes, I will continue using the Marvel Comics comparisons here because, goddammit, that's what it is in my mind!) and the LoSverse. With the original timeline, you have 25 years and several different people's contributions to muddle through in terms of ironing out a coherent story, let alone one without plotholes. Then IGA came along and (as odd as it is to say) tried to tie them all together in some fashion. While it worked in some places and really didn't in others, it was still a difficult process. However, when you think about it, the original writers for Castlevania probably didn't intend to have this huge flowing storyline attached to the games. They just made the first game for what it was, then tacked on Simon's Quest and Dracula's Curse with as much story as either needed to be plausable, and move on. And so on, and so forth.
So now we have the LoS universe potentially making gaping plotholes, when the writers really are trying to make a huge flowing storyline attached to their game. Should this be excused any more than the plotholes in the original universe, because of the difference in circumstances?
I know, it's total speculation at this point and we're probably making far more of it than it will actually be. (What can I say? I love debating in-depth storytelling and stupid shit like that) But hey if MS and Cox (or hell, throw IGA in there too) happen to read any of these topics and posts and whatnot, they'll hopefully see that coherent plot and storytelling really is seen as an artform in and of itself by some of us.
I'll stand as a proponent of that always.
