I think this article demonstrates very well why I think React should be the first choice for any new web projects... what to go with it (ember, flux (and related), or other) is open to more debate.
Of course there are great alternatives with similar workflows (mercury, etc).
I think this sums up React.js perfectly. Easy to learn and build something with, but the discussion around Flux and what libraries to use to implement it can complicate and deter newbies. The official explanation of Flux on Facebook's own site I think does a poor job explaining it in a way most developers (new and senior alike) can understand.
That's very fair, it gets even more complicated when trying to do server/client mixed rendering with it. It's all very hard to grasp in a deeper level.
This tutorial is absolutely awesome.. and I think the deep dive is worth it for larger apps too.
Of course there are great alternatives with similar workflows (mercury, etc).