Ask HN: To use or not to use React?

I recently hired a developer to work on a web application I wrote in my spare time over the last two years. After having a look and pointing out several of the flaws, the developer suggested we rewrite the project using React. The web app currently relies on HTML, JavaScript, and CSS for the front-end. What are the pros and cons of using one versus the other? Is React preferable in any way to HTML, JavaScript, and CSS?