In short, it's simple (very little to learn) and very fast. One other big thing I love is that it encourages building reusable and composable components. Angular has a lot of the same structure, but if you end up building directives then you have to drop down to manual DOM manipulation again if you want speed.
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I wrote a little bit about my experiences here:
http://benalpert.com/2013/06/09/using-react-to-speed-up-khan...
In short, it's simple (very little to learn) and very fast. One other big thing I love is that it encourages building reusable and composable components. Angular has a lot of the same structure, but if you end up building directives then you have to drop down to manual DOM manipulation again if you want speed.