One of my favorite things about React/Redux ecosystem is that it pushes you to learn a lot of best practices within javascript such as smart use of functional programming, immutability, and modularity.
Is it a fad? Well almost every javascript framework eventually feels like a fad because people are so crazy good at innovating on the frontend very quickly.
Last year everyone was complaining about this and saying they were getting javascript fatigue. I for one love the innovation and am excited about new developments, but it can become taxing feeling like as soon as you've picked up the new hotness, it's already old. Which is why javascript fundamentals are key to staying relevant and not getting too frustrated with the churn.
React has a pretty steep learning curve simply because of all the things you usually end up using in a project. React itself is relatively small but most everyone now uses React/Redux with a ton of middleware and addons to make development more scalable, and everyone is usually transpiling with babel/traceur to get ES6/ES2015 features.
Not to mention lots of boilerplates are using webpack which is its own beast. So I would definitely first focus on javascript (ES5) and then once you're comfortable with those basics I would move onto learning ES6/ES2015 features. Then getting into react or any other new framework coming out in the next few years won't feel so heavy to learn. You can see by inspecting this very site that they built it with react :D