I spent a lot of time looking at JS libraries and frameworks. From jQuery, to Knockout, to Backbone, to Angular, to Batman, before finally settling on Ember. I am extremely skeptical about the need for more frameworks.
I usually don't give a new JS framework more than a couple of minutes to introduce itself. If it does not look like it will revolutionize how apps are built, I quickly write it off as a slightly different way to slice the pie.
Right now the clinet+server-side (isomorphic) story for a lot of these tools is less than outstanding... React, or something like it will likely win in the end. Although I've also been keeping an eye on mercury, riot and polymer. Angular 1.x was too annoying in practical use, and wrt Angular 2, may as well just use React.
Have you checked out Meteor.js and skit.js? They seem to me to be the frameworks currently most geared towards reusing code on client and server (e.g. isomorphic - sorry mathematicians).
I've looked at Meteor, and haven't looked into skit... admittedly when I looked into Meteor very early on, I didn't like their security model (or iirc lack of).
May take a look again... also, it seemed to be very tied to mongodb, which I didn't mind at the time, but am moving away from.
I usually don't give a new JS framework more than a couple of minutes to introduce itself. If it does not look like it will revolutionize how apps are built, I quickly write it off as a slightly different way to slice the pie.