Wait a minute, is this a troll post? Interfaces? I get the tooling, maybe, and CSP out of the box, I don't understand what's great about Go's interfaces (compared to plain old boring Java, for instance).
Yup. I literally just gave a talk at two Go conferences in the last two weeks (GopherCon India and GopherCon Dubai) about the io.Reader/io.Writer interfaces specifically. They're deceptively simple on the surface, but they're insanely powerful once you 'get' them.
There was a blog post a while ago about how golangs's interfaces caused issues in production because they're implicit.
Check out type classes for a superior way to solve this issue (e.g. what Scala or Rust do).