So, basically, I've embarked on every writer's nightmare and am writing a multi-(6)-part fantasy series. I've completed the first book (currently on its third draft, and I'm very satisfied with it, yay!) and soon I'm going to start work on the second one, while seeking publication on the first. I've outlined the entire series in advance, knowing roughly what's going to happen in each book. (Rowling did similar, though I'm hardly a Rowling, at least not yet if ever.) The trouble is that I have a lot less faith in the second book than I have in the series as a whole. I haven't written it yet, but I have a bad feeling about it; from my outlines, I have a hunch that it's going to be the weakest in the series, and the weakest in a long series being the second one might kill the series. I mean, maybe it's not going to be bad and I'm just worrying about nothing, and it'll all really come together when I actually write it. But should I try to improve my outline until I feel confidence in my project before I start, or should I dive in and try to make it coalesce in the actual writing? For reference, the reasons I'm nervous about it from the outline are: 1. The antagonist of the second novel specifically is the only aspect of the series that I did not originally conceive for the series; it's an older nightmare of mine that I imported to the series because I thought it'd fit with the second book. I'm not entirely sure now whether it fits with the rest of my world or is out-of-place, because I could see my personal knowledge of my thought process biasing my decision either way. It could seem a little cheesy for the relatively dark tone of the series as a whole, or it could be perfectly dark enough. Either way, it's a relatively insignificant concern compared to the way that... 2. Although the novel's narrative leads naturally to exposition relevant to the series as a whole, it's fairly self-contained and does not directly advance the series-wide narrative. This is deliberate, not an oversight on my part; I'm personally fond of the idea of the novel being a detour from the "main quest", but am worried it might turn off readers, as might the fact that... 3. Large chunks of the novel are flashbacks in the life of a secondary character. I see nothing wrong with this, personally, and I think it contributes a lot to the narrative as well as the atmosphere. However, it's a departure from the series' generally limited focus on the protagonist, so it just generally contributes to the feeling that... 4. It's basically just the odd-man out in the series. It's a single entry in a six-book series that feels a little off from the other ones.
Hi, welcome to the forum. I'll give you the standard answer, the idea is only a small part. It's how you write the story that matters. If you're happy with book one, and not book two, put book two aside. Promote book one, be sure the readers think it's as good as you feel about it. Start on book three and come back to book two after a break. It's one option. There are other ways to address your issues.
This sounds to me that what you're actually writing is a 5-part series, with a further novel written within the same universe. A bit like LOTR & The Hobbit. So do that, as GingerCoffee says, go straight to book 3, and if the series takes off, you've got a ready-made next novel to cash in!