This book has three distinct themes to it. One is Henry David Thoreau's love of nature and his view of it as a balm to the soul. The second is that he seems to think that those who work the land hard are fools wasting their time, that they should do only what it takes to survive off the land. And the third is his attitude towards government and democracy and his opinions regarding disobedience of authority.
The first theme gets a bit played out over the length of the book, and Thoreau himself eventually tires of nature and moves on from Walden.
The second theme is an elitist position, and it may very well be that Henry David Thoreau didn't have to work very hard to live off his bit of land - but he seems to have no concept of how those who made his silverware, cookware, etc. are fed.
In regards to his attitude towards government, democracy and disobedience of authority - I would just say that I find myself mostly in agreement with Mr. Thoreau.