I was going to make this just a comment in Ty’s post, but I think it deserves it’s own headline.
In a comment, “TheTick” said:
Your typical player of sports who the mainstream media says is having such a slump is almost always facing stiffer competition with less help and more responsibility.

John Simm: Daniel's to play Daniel Abraham in the VH1 Where-Are-They-Now reenactments.
My take on the “sophomore slump” for writers — and especially for those of us writing series — has more to do with reader’s expectations than the actual quality of the books. When the first book of a series comes out (or the first episode of a television series, or — memorably — the first chapter of a book like Lucius Shepherd’s A Handbook of American Prayer), I get all excited. I start preparing myself for the ride that I’m on. The thing is, my idea of where things should go and author’s idea are wildly unlikely to match up perfectly.
I remember watching the first season of Life on Mars — the real one with John Simm — and actively rewriting the show as I watched it to the point that I don’t remember the *actual* show as much as my self-built private version. The creative forces on it didn’t go where I wanted to, and so I was disappointed. After the first episode, I had already pointed myself in a direction similar to, but not precisely aligned with where they were actually going.
The books are the same. Just to take an example, in The Dragon’s Path, I introduce a minor character — Clara — who gets to be the center of a couple of chapters. If her role expands in the second book, some folks will feel disappointed. If it doesn’t, there will be some folks who are disappointed. Over in Carrie Vaughn‘s Kitty Norville series, Kitty forms a serious romantic attachment with one character rather than another, and the partisans of the guy what didn’t get the girl are always going to feel that discomfort.
It’s a fine line, and some ways it’s not fair. As an author, I’m asking readers to invest in the world I create, believe in and care about the people in it (oh, and pay me while they’re at it), but I don’t want them to take any control.
I think the sophomore slump is all about reacting to the real necessity of making narrative decisions, and wrestling with the fact that they can’t all be the decisions that all the readers would have made. Readers aren’t monolithic, and there are going to be some who would prefer I’d done it the other way. No matter which way I go, there will *always* be folks who would have preferred the other way.
Which, I think, is why we have fan fiction.
Fan fiction is where the readers can appropriate the world and characters and tell the story they way it is in their heads. When I was talking about re-editing Life on Mars, I was basically making a little fan fiction version of the show for an audience of just me. It was a freaking good show not because it was better than the real one, but because it was tailor-made to push my buttons. I know. I was the tailor.
So I’m worried about Caliban’s War and The King’s Blood, but not because I don’t think they’re cracking good books. I think they’re better in some ways than Dragon’s Path and Leviathan Wakes. But part of what makes them good books is that they make decisions. They change their respective stories. Things happen, and there will always be readers who would have made a different choice. There’s literally nothing I can do about that except tell the story I’ve got as well as I can, accept that there will be a few grim reviews of the second books, and start writing The Poison Sword and Dandelion Sky.