My personal favorite poem by Walt Whitman is "When Last in the Dooryard Lilacs Bloomed." The poem is just so sad and beautiful that even with its abnormal length, I still wish it was longer. The poem was written about the death of Abraham Lincoln, who Whitman greatly admired. He writes about Lincoln's death as one would the death of a great friend, and because of this the poem has a very sweet sort of melancholy. I really love how sad the poem is, even though it is sort of a contrast to all of the joy contained in Whitman's other poems.
In one part of the poem that I particularly love Whitman describes death as his companion, walking on one side of him, and the knowledge of death as the companion on the other side. As he and his sad companions are out, they listen to the sad song of a bird, whose song Whitman interprets in his verses. This part is particularly sad for me, and the imagery is so vivid that I can easily imagine myself there. He also writes about death as a peaceful release from the troubles of the world, and sings a brief praise of it.
I know it may be a bit shallow, but I also like the poem because of its mention of lilacs. When I lived on Lake Petersburg, there were lilac trees all around the house, and they made the entire place smell beautifully. I never really liked them until a year or two after we moved away, but now when I smell them they remind me of my home, and I love them because of it, even if it does make me very sad now. The poem makes me wonder if I am not the only person who has sad associations with lilacs. Also, the way lilacs smell is so sweet and unique that they are perfect for a tender poem about the death of a friend.