World-Building: Too Much, Not Enough, or Just Right?

So, in the ongoing agent search, I found several agents who mentioned the same thing: books that started off telling everything about the world, instead of advancing the story.  Apparently, a lot of people who submit their first five (or ten, or twenty) pages have a habit of getting the story started and then laying on the backstory and history with a trowel.  Possibly with a shovel.  And this got me thinking:

I write fantasy.  It's about the only thing I've ever wanted to write, and recent attempts at novels have taught me I just don't belong in the real world.  ...writing in the real world, I mean.  But since writing fantasy means working in a world that doesn't exist, there's always the issue of making sure the world you're working in is defined enough.  You don't want the reader to be lost, or feel like it's all happening on an empty stage with a few cardboard trees and a dragon made of duct tape hanging from a length of twine in the background.

Two books I read last month took very different tacks on this whole world-building thing, and the sheer contrast makes me think of Goldilocks and the Three Bears.

The first book had Not Enough background info.  It was a fantasy novel in which some people had a distinct connection to the land and there was some kind of council of them whose job it was to make sure things didn't get horribly screwed up and the land didn't rebel against them.  If this sounds vague, it was - I don't even know how many people were on the council or what their roles were, as most were very ill-defined, and the book focused on only two or three of them.  While the book itself was worth reading, I found myself constantly wondering who these people were and why they were important.  When the lack of background detail and explanation means the story's events fail to have the intended impact, something is wrong.

The book that got it Just Right drip-fed a steady stream of background info as it came up.  The story was based around a military and its operations, so whenever they went to a new place, or dealt with new people (for various definitions of 'people'), we learned a little more.  By the time the book ended, I had a great picture of how the army operated and the worlds it worked on.  All without resorting to an eighty-page infodump.  The fact that the narrator was old and cynical but still amazed at all the stuff he was getting into helped a great deal.

As for a book with Too Much background and world-building... Well, there's only one thing I can say, and I say it with the utmost respect: Tolkien.  Moving on.

While I doubt I'll ever write military-based sci-fi, I know I'll keep that book in mind as I work.  Most of my plots involve significant world development and backstory, so I'll look for a way to get it to the reader as it's necessary, pace it out same as I would the plot. As I say about everything I write, hopefully it'll work.

Next entry: what do you do when you realize you're ripping yourself off?