As I've mentioned before, one of the major goals in my current rewrite for my novel is to deepen the level of detail in the world. It's important that the reader be taken to this alternate universe I'm creating, that they can see the texture of it, believe that it's real.
Interestingly, though, working the details into the text hasn't made it much longer. I'm finding that it's a lot more about focus, how you can weave the information into the action and dialog that's already going on. When you can drop those little hints that speak subtly to the reader, that's satisfying.
Not to say that I'm anywhere near mastering this, but it's good fun learning. In the first chapter, one of my critique group members pointed out a nice expository paragraph that I had plunked down. Good information, but totally dead on the page, "Why are you telling me this?" type of stuff. Her suggestion for fixing it was excellent as well. For example, if you have a science experiment in scene, and it is actually important that the reader understand it, don't just describe it. Have something go wrong. Show the scientist struggling with it, having conflict, messing it up. By imbuing the experiment with that additional tension, you've got a meaningful structure in the story for explaining the more mundane details you need to get across.