When I'm reading (or watching), the story could be utterly ridiculous and unbelievable and I'll still soak it all up. It could be the silliest premise on the face of the planet, but I will read on: Provided that the characters are compelling.
Without good characters, even the best premise will fall flat. The world-building could be a marvel of the ages. I won't care. If the characters are little more than chalk outlines, all the fancy words and brilliant worlds and cunning plots in the world cannot save the book from being closed and never even glanced at again.
The Beka Cooper series by Tamora Pierce is a fantastic example of this. It's written in the first person, which I generally dislike reading, and it's young adult, which I also generally dislike reading, but I love this series (so far. I've read two of the three). Despite everything working against it, the characters in this series are so rich and compelling that I gobble it all up happily.
The Malazan Book of the Fallen series by Steven Erikson is another series that does characters brilliantly. In the first book Gardens of the Moon, and I know I've spoken of this before so sorry for the repetition, there is a character - Anomander Rake - I started off hating. By the end of that book, I felt so sorry for him, and just wanted to run up and give him a long, tight hug. He needs it. This brilliant twist was achieved by writing character well, by acknowledging that good and evil are not opposite ends of the spectrum, but facets of the same coin, by acknowledging that everything is just a shade of grey.
And gods do Pierce and Erikson manage that well!
Characters do not have to be complex in order to be full, either. Too much complexity and the whole character unravels entirely into a confused mess of a person. Take Roland Deschain of Gilead in Stephen King's The Dark Tower series. He's a very simple man. In fact, it's his simplicity that makes him so compelling.
He is a man with a single purpose, and all else falls to that purpose - including loved ones. It's this that makes him so compelling. It's this that made me feel for the guy. It wasn't complex angst that made me want to reach into the book and draw Roland into a hug, it was his simplicity. Somehow, that simplicity of character gave him incredible depth.
Generally speaking, for my own work, the first thing that I have finished before I start writing is character. I know the protagonist intimately before I sit down to write, and that character informs everything that goes down on the page. Character, for me, is the most important thing to get right.
This isn't the same for everyone. I know plenty of readers who cannot read unless the world-building is fantastic. They don't really care how silly the premise, nonsensical the prose or shallow the characters, if they can fall into a world, then the story is good. Others still can't read a book if the premise is silly, even if everything else is absolute perfection.
It depends on the reader. I am intensely interested in psychology; what makes certain people tick? Why do they do what they do? How do they cope with their situation? Really that's all I care about.
How do these people cope with all the shit they go through?
Clue: some better than others. Looking at you Commander Skye and Prince Cai. Ahem...
Anywho, what do you read for? Character? World-building? Good science? Let me know! I'm interested.
Alright, I must work.