Preface: Before learning any JS framework you need to have a solid understanding of the language. Period.
Now that I'm off my soap box, this is going to be a bit of a complex answer but here's TL;DR: React is a fad/flavour of the day but it's also here to stay and is an important tool.
So, before I get flamed to death, here's my reason why React is a fad/flavour of the day. It's new(ish). It's what all the cool kids are using; much like when Angular was the new hotness.
Now, does that mean React isn't worthwhile? Nope, not at all. React is getting people excited about developing in a new way much like the older SPA frameworks such as Angular did a few years ago. It's an important tool in an ever growing toolkit.
The rising React star like JQuery/Angular/etc. before it will decline. It's the nature of web development, but that doesn't mean you should ignore it. Web frameworks and technologies cycle and evolve and in 3-4 years we'll all be talking about SPLONK.JS or something that makes React look ancient by comparison. That doesn't mean that it's not worthwhile to learn it and just because something new and shinier comes along doesn't mean that React will suddenly stop working. Thousands of sites still use and are still being built in Angular 1 despite Angular 2 being more or less here.
So yes, React is the flavour of the day. All the best frameworks/libraries were at some point. Dive in, have fun, and add it to your tech stack. You'll only make yourself a better developer at the end of the day by expanding your horizons.
Just make sure you:
<soapBox>Have a solid understanding of JavaScript before trying to using any framework or library</soapBox>
I don't know how many times I've interviewed developers that think making an ajax call involves $.ajax() and have no idea what XHR is.