What's up with Leaves of Gr?

I picked it up in a B&N today, it is really messed up. The first 50 pages are the original, and the other 250 are the "deathbed edition". Walt Whitman must have been high when he wrote this book. The poetry wasn't that good either, just a bunch of sappy poems, many about death. My English teacher always freaked about this book, but I want to know what the big deal is.