Andrew Gelman has a post about this interesting tool to visualize text sentiment, created by one of his students. The example he provides is below. I have three comments.
1. The opening of Moby-Dick is the greatest opening of a novel ever.
2. "Deep neural networks" appear to have some difficulty gauging sentiment. The lengthy fourth sentence has a quite negative tone, unless the software is picking up on the humor. Some of the sentences it identifies as strongly negative seem relatively cheerful to me, by comparison.
3. Conclusion: This text sentiment visualizer needs to read more great literature!