So I'm a bit torn on this one. Regarding this:
I do see the merit in trying to prevent authors from making big tonal shifts
I don't see any merit in preventing authors from doing anything. While I get that it can be annoying for readers to "have to deal" with something like that, framing it this way sounds - at least to me - like trying to limit the creative freedom of authors which I am absolutely against. A site that's meant for authors to upload their original series on should not limit the creativity of the authors after a certain point (that point being the law and ToS of the site).
But, on the other hand, I do agree with this:
I love it! This sounds like a very fun feature.
It does sound like a fun thing that could add to the ability of readers to search for something they'd like (or are in the mood for) which I think is good overall. Personally, I would even use it as a reader every now and then. Although I'd probably still go with the general series finder most of the time. I could imagine this being another option in the series finder though? In fact, some of the tags like 'heartwarming' and similar could probably be migrated over without much of a hassle?
What I'm not quite happy with (yet) would be this:
Just make it mandatory to fill out before they can make a new novel
I get the point that if authors don't use this, then it wouldn't make much sense to implement it. But honestly, even after reading your examples above, I still have no effing idea what the fuck "noble dark" is supposed to be and I've read at least one-third of LotR. It is often hard enough to find useful tags that adequately describe a whole series. Adding some obscure 'mood' makes that even worse and I, personally, might just click on anything to be done with it even if it doesn't actually fit the story. You'd need some
very specific explanations (and those are shit even with the tags already IMO) to make this work.
And this is coming from somebody who is
not a new author. New authors - I'd imagine - might struggle even more. They have to come up with a title, a cover, a blurb (never understood the want for a synopsis, actually, I'm all for blurbs!), choose the right tags, ... and now also a mood? I think this might be a bit too much to ask of them.
Also, even if we say that readers can vote on the mood (instead of authors choosing that) and ignore possible trolls: Readers often rate and review stories when they have read barely anything. With the overall mood of a story that they vote on, this might be even worse because they
feel like what they vote for is the actual mood of the story but it might not be.
Like, personal example: My main series has about 12 volumes or so with each of them being 150k+ words so I'd consider it fairly long. It starts out as this very quirky, comedic thing because the plot seems absurd and the ML is batshit crazy. Mood for that one after reading the first couple of chapters? Probably something happy or heartwarming.
Problem is: It starts to slowly shift into a much, much, much more mature story after the first 100 chapters or so. The story deals with the loss of loved ones, murder, and mental health, ethical questions, star-crossed lovers, unrequited love, betrayal, depression, abusive relationships, ... the list goes on. It's a downright
tragedy for large parts of the series.
And no, those aren't any abrupt shifts in the tone of the story. They're hinted at, at the very beginning of the story and slowly manifest themselves. They get more frequent but that doesn't mean that there isn't still the quirky, comedic tone below that. They're both there for most of these volumes and they were
both planned. Like, this isn't something I did accidentally, it's how the story is supposed to pan out.
Now, if this feature was to be implemented in either way, I see a big problem:
I wouldn't personally know what overall tone to choose. People who expect something serious would be put off by the first few chapters if that's what they were searching for and people who come for the happy, fluffy, quirky romance would throw the thing away because that's not what they signed up for. The story is, for all intents and purposes, both of these and that from the beginning to the end. By adding a single mood, I'd be misleading the readers instead and make them have expectations that I just can't fulfill because that's just not the story I'm writing.
If readers are the ones to vote for the mood, more than half of them would vote while still reading the first volume and give a vote that doesn't cover the full series. And I - as the author that fully knows that this isn't right - would be without any way to do something about it other than adding a note to my blurb which shouldn't be the intention. I mean, I'm pretty sure the blurb already hints at it enough as is.
So, to summarize (the
TL;DR for you lazy people): I do see this as a feature that could be fun but I find it too restrictive with how it's presented so far. It certainly works great for shorter works where huge tonal shifts are likely not going to happen but it can't really account for longer series where those tonal shifts are
intended and actually a major part of the story's appeal. I think that there would be the need to at least allow for more than one mood to account for that but that might result in having stories with quite the strange mood cluster.
Also, letting readers vote sounds good in theory but could - once again especially for longer series or even series that update less often or regularly - be a major pain in the ass because readers might vote too soon before they actually have a good grasp on the actual story and its mood.