I like that Underscore.js provides a good foundation for building out your JavaScript programs. It has a lot of useful utilities that make it easier to write readable, maintainable, and testable code. I dislike that it is not included by default with Node.js. It is a bit more difficult to get started with than other libraries that are included with Node.js. I am using Underscore.js to build out a number of JavaScript programs. I really like how easy it is to use Underscore.js. It makes it very easy to write readable, maintainable, and testable code.