Does simply breathing qualify as living? Or does living require far, far more? In Walden, Thoreau examines his fellow man, and finds him wanting, lacking, unfulfilled: laboring day in and day out, trapped by the desire for wealth and material comforts, unable to distinguish between luxury (like butter and a house with more than one room!) and necessity. Most men, according to Thoreau, are trapped in a kind of living death that suppresses everything that is natural and wonderful about being human. Talk about dark.
But Thoreau is trying to rescue us through Walden. This book is an attempt to break past all our misconceptions about the true meaning of life, and get to some understanding of what real life is. Life isn't just about going through the motions in your daily grind, but enjoying all the faculties for thinking, imagining, and feeling that are unique to each and every one of us.
For Thoreau, life requires a capacity for judgment and understanding that has withered away in modern society. Basically, we're in bad shape.
In Walden, waking up is a metaphor for opening our eyes to the possibilities for the good life all around us.