It's not bad... it's just much more light-weight (essentially). So, the bigger the project, the more you're going to feel Backbone strain relative to AngularJS. However, for small projects, you probably don't need such big guns... but if you can afford shipping AngularJS to the clients anyway, why not?
You can see the different styles for yourself for a very basic web application (and try to extrapolate what it would look like for large ones): http://addyosmani.github.com/todomvc/
The difference between Backbone and Angular is that AngularJS is more like Rails whereas Backbone would be more like Sinatra. What it means is , for complicated apps , you'll have to do complex stuffs anyway , so 'complicated' features are better built in the framework itself.
Unless you use a plugin , you'll have hard time updating your views automatically in Backbone if your model has nested objects. And your models cannot be arrays. In AngularJS it doesnt matter.
Backbone is not like Sinatra. Backbone is a hell of a lot more work than Sinatra. Backbone is a framework that more easily can fit atop existing design and services, however it takes so much time and in the end you just have even more complex spaghetti for someone else to maintain when you leave.
You can see the different styles for yourself for a very basic web application (and try to extrapolate what it would look like for large ones): http://addyosmani.github.com/todomvc/