A beautiful, descriptive paragraph draws me right into a book, but it isn't what keeps me reading. If a book is filled with paragraph after paragraph of setting description then I'll eventually get bored. There has to be action or tension of some kind that keeps me reading. Don't get me wrong, I love it when an author gives such a vivid description that I feel like I'm there, but even that can be over done. As writers we have to find the happy balance between action and describing the setting.
How much is too much? Any time you describe the setting the reader shouldn't feel like the action or tension has stopped. Instead, the setting should add to it and help propel the story. If your protagonist is feeling blue it might help to have it raining, or make the room they're in dark and dismal, if they're mad you could have a storm approaching or make the room chaotic and messy. Your character's environment will reflect them in some way because what they're feeling and going through will affect the way they see it. Contrast can also work for you if you do it right and have the character responding to how the environment is clashing with them.
Have fun with it, try a few writing prompts and try out setting and mood. Just remember, don't stop the flow of tension or action. The story must go on! As with everything in your book, if part of your setting description doesn't move the story forward or add to it in a necessary way, it isn't needed. Join us this Thursday, 6pm PT on Twitter for the #WritersRoad chat where we'll discuss this in depth.