Here are the list of points from the FAQ :

The focus is on supplying you with helpful methods to manipulate and query your data, not on HTML widgets (angular) or reinventing the JavaScript object model (Ember).

Backbone does not force you to use a single template engine (Ember). Views can bind to HTML constructed in your favorite way.

It's smaller. There's fewer kilobytes for your browser or phone to download, and less conceptual surface area. You can read and understand the source in an afternoon (Ember and Angular).

It doesn't depend on stuffing application logic into your HTML (angular / knockout). There's no embedded JavaScript, template logic, or binding hookup code in data- or ng- attributes, and no need to invent your own HTML tags (angular).

Synchronous events are used as the fundamental building block, not a difficult-to-reason-about run loop (Ember), or by constantly polling and traversing your data structures to hunt for changes (Angular). And if you want a specific event to be aynchronous and aggregated, no problem.

Backbone scales well, from embedded widgets to massive apps.

Backbone is a library, not a framework, and plays well with others. You can embed Backbone widgets in Dojo apps without trouble, or use Backbone models as the data backing for D3 visualizations (to pick two entirely random examples).

"Two way data-binding" is avoided. While it certainly makes for a nifty demo (Angular & Knockout), and works for the most basic CRUD, it doesn't tend to be terribly useful in your real-world app. Sometimes you want to update on every keypress, sometimes on blur, sometimes when the panel is closed, and sometimes when the "save" button is clicked. In almost all cases, simply serializing the form to JSON is faster and easier. All that aside, if your heart is set, go for it.

There's no built-in performance penalty for choosing to structure your code with Backbone. And if you do want to optimize further, thin models and templates with flexible granularity make it easy squeeze every last drop of potential performance out of, say, IE8.

I have marked the individual points he pointed out with the relevant MVC framework out there.. I might have missed out on some but it looks like ( atleast to me! ), jashkenas feels the greatest threat to Backbone currently is Angular.. And I think he is right about it.. Backbone is currently ruling the throne of Front End MVC frameworks, but it looks like its rule is ending soonish...