See this discussion [1] with the response from rauchg (framework author and Zeit founder) outlining where they are heading.
This ability to easily mix SSG and SSR pages within the one project, the PHP-inspired philosophy of simple file-based routing for pages, and pre-configured babel / webpack with easy customisation are a few things that draw people into next.js dev.
Like anything that deals with reasonable complexity there are a bunch of concepts to understand, but once that happens next.js feels like a thin layer around "it's just react".
I particularly like being able to drop api functions with a standard req / res signature into `pages/api` to immediately have some server-side api endpoints available, which can be deployed to Zeit's now as Lambdas with minimal fuss. It significantly reduces the friction of thinking about and implementing front-end sites with custom api endpoints for whatever you're building.