Every moment of a science fiction story must represent the triumph of writing over worldbuilding. Worldbuilding is dull. Worldbuilding literalises the urge to invent. Worldbuilding gives an unnecessary permission for acts of writing (indeed, for acts of reading). Worldbuilding numbs the reader's ability to fulfil their part of the bargain, because it believes that it has to do everything around here if anything is going to get done. Above all, worldbuilding is not technically necessary. It is the great clomping foot of nerdism. It is the attempt to exhaustively survey a place that isn't there. A good writer would never try to do that, even with a place that is there. It isn't possible, & if it was the results wouldn't be readable: they would constitute not a book but the biggest library ever built, a hallowed place of dedication & lifelong study. This gives us a clue to the psychological type of the worldbuilder & the worldbuilder's victim, & makes us very afraid.
M. John Harrison
The Cloud Roads has wildly original worldbuilding, diverse and engaging characters, and a thrilling adventure plot. It's that rarest of fantasies: fresh and surprising, with a story that doesn't go where ten thousand others have gone before. I can't wait for my next chance to visit the Three Worlds!
The key to good worldbuilding is leaving out most of what you create. You, as the author, had damn well better know the where all that dragon food comes from, but that doesn't mean that I, as a reader, want to read a five thousand word essay about you explaining it to me. I don't need to see the math, but I can tell by the details you provide whether or not you've thought these things through to their logical conclusions.
Also, worldbuilding touches all aspects of your story. It touches plot and character as well. If you don't know the culture your character comes from, how can you know what he's really like? You must know your characters on a much deeper level than you would if you just shrugged your way into a cookie cutter fantasy world.
I enjoy worldbuilding very much. I generally start with an approximation. With 'Flesh and Spirit' and 'Breath and Bone,' because I was thinking of a world on the brink of a dark age, I began with the sense of Roman Britain. But I purposely set the geography to match something other than Britain - which has been overdone.
Though in this genre we write about the fantastic, the stories work best when there is solid grounding in our world. Magic works best for me when it aligns with scientific principles. Worldbuilding works best when it draws from sources in our world. Characters work best when they're grounded in solid human emotion and experience.