Well, here are some of the features that made Angular popular, IMO :

1. The two way data binding feature. This was inspired by the data binding feature available in Adobe Flex. Most importantly, JavaScript developers never used to write model driven browser apps. Angular taught them how to do so. Naturally, it was an instant hit.
2. It made super easy for developers to write apps that leverage HTML5's pushState API and thereby allowed them to integrate routing into apps very easily.
3. Templating is also very simple with AngularJS. The double curly braces have helped developers more than anything else.
4. Advanced developers love to write tests while developing apps. Angular gave them a great testability story with Karma, Jasmine and Protractor setup.
5. Besides all these Angular helped developers give structure to their apps by offering an MVW architecture (You know it already!).