Framework supports a good security elements. Automatically encodes received data and checks incoming requests.
You can extend framework by yourself. You can rewrite existing functionality and replace it according to your needs.
Framework has unique templating engine. It's beautiful, simple and powerful. Templates is a strong weapon for the web development.
Define a different actions to one url and distribute by e.g. HTTP methods. Framework has the best routing engine as you know.
Framework supports WebSocket (RFC 6455) and Server-Sent events. You can create real-time applications or multiplayer games.
Framework has an easy learning curve. You will learn to create web applications for a very short time.
Install once and run anywhere - Unix, Linux, Mac OS X, Windows or SunOS. You don't need other applications for your website.
Framework has good architecture for big applications and on one project can work more developers.
Framework is licensed under the MIT license which makes it perfect for use in commercial applications.