Although both of these poems show respect and affection for the natural world, I would say that Keats's poem is much more positive and Dickinson's is much more negative in its view of nature.
In Keats's poem, the tone is one of admiration and happiness. We see that, no matter what, there is always life in the natural world. We are told that the poetry of the world, the beauty of life, never ends.
In Dickinson's poem, by contrast, there is a fear of nature. The speaker can admire the snake, but that is not the main point. The main point is that the snake always inspires fear in her.
So Dickinson's poem is much more negative -- its main idea is the fear that nature can inspire, not its beauty.