* Streamlined language with carefully-chosen syntax and keywords (there aren't 10 different meanings for "static", for instance); entire concepts have been eliminated to no apparent ill effect in building real systems. Fewer cycles allocated to the language, more cycles allocated to problem domain.
* The 95% case for associative and sequential containers is built into the language, with (for me) enormous benefits to programming efficiency.
* A streamlined and carefully orthogonalized standard library optimized for systems programming. Golang has the best-designed standard library I've ever used.
* A ruthlessly pragmatic packaging and modularity system; unlike C++, packaging is not left up to the build system.
* Build-world compilation times measured in 100s of milliseconds rather than 10s of minutes.
If I was writing, say, a generic trie library that I was hoping to get hundreds of different programmers to use, C++ would be a tempting target because of generics. But it turns out, most of the time I build projects like that, I'm really just wanking. Another benefit of Golang is that it's so stripped down and pragmatic that it subtly discourages wanking.
A lot of people would add Golang's concurrency model (share by communicating instead of communicating by sharing) and lightweight threads to this list. I like Golang concurrency too but my sense of it is that among languages designed from the jump for concurrency, this isn't that much of a unique benefit.