Here's a long list of examples why maybe it should be:
http://backbonejs.org/#examples
In comparison, here's the public list of interesting apps built with Angular and Derby:
http://builtwith.angularjs.org
https://github.com/codeparty/derby/wiki/Community-Projects
What you want to look for in a library goes beyond feature checklists and magic datepickers. Lots of client side developers have been burned in the past by JavaScript frameworks that promise the world and end up getting in the way more than they help.
Backbone tries to provide the barest useful essentials -- the main business of building your app is up to you.