Good question. And one I can't easily answer to be honest. In most respects I suppose this is very much a subjective matter.

For me it's the language's simplicity. There are no hidden surprises in the spec. It's short, clean and easy to memorize. The syntax is clear and (for the most part) un-intrusive. Some of it's idioms really force you to think about what you have learned in other languages. And then either forget any of that ever happened, or at the very least become a critical thinker about the usefulness of these things. For example: the standard inheritance based OOP model.

Go simply allows me to 'get shit done' fast and without having to jump through hoops. It's very much like a breath of fresh air in what was quickly becoming a stale and obnoxious development environment (for me at least).

Edit: I would add that I do not particularly like evangelising about anything; that includes Go. It is beautiful for what it is. but by no means should it be considered a silver bullet. If your current tool chain(s) and language(s) work for you, by all means continue to use them. Go has its strengths and its weaknesses that should always be considered at the same time.

The right tool for the right job and all that.