Fast Learning Curve
React is very a simple and lightweight library that only deals with the view layer. It is not a beast like other MV* frameworks such as Angular or Ember.
One of the powerful sides of React is that it provides a good abstraction which means that it does not expose any complex internals to the user.
Flux and Redux
Flux architecture is introduced and maintained by Facebook and they use it for their web applications. It complements React components by unidirectional data flow.
Fast render with Virtual DOM
React provides a component based structure. Components are your lego pieces. You start with tiny components like button, checkbox, dropdown etc. and the you create wrapper components composed of those smaller components. And then you write higher level wrapper components. And, it goes on like that until you have this one root component and that component is your app.