I have done a large Backbone.js project for my last employer. I was on that for about 18 months. I have not done a project with both Backbone.js and AngularJS in the same project. I know some people do that but I truly cannot think of anything Backbone.js brings to that party.

As for Backbone.js by itself... It's OK, I liked it but we had a large project with as many has half a dozen people working on it at its peak and the problem we got into was all of the huge gaps in Backbone.js that you typically fill with other software (two-way binding, validation, templating, AMD, etc.) and if you don't figure out your solutions for all of those gaps before you start every developer in the group ends up filling it his or her own way. Especially if you're under a time crunch and writing really fast.

We ended up with a working project at the end and it was way faster than their old solution but it was a chimera. Every part of it appeared to be a different animal. With AngularJS a lot more of those parts are part of the framework itself and there's less room for that kind of problem. I'm using it for large project work now and liking it a great deal more.