This interested me as well. In particular since we have developed quite a few medium sized projects in Go (20.000-50.000 LOC) and, in my experience, it is more pleasant than, say, doing it in Java or C++.
In my experience, with both C++ and Java there is always a discussion of style, frameworks and practices. Especially in C++ those choices have big consequences since C++ isn't just one language: it is every snapshot of the language for the last 20 years. If your project requires the use of a library, your code has to adapt to choices made for that library.
Java has different problems. Higher level problems. It isn't so much about which features aren't available/usable/advisable, but about what framework you use. Most people don't really work in Java, they work in various Java frameworks. And some frameworks are like herpes of programming: if you start using them in a project, you can never get rid of them. At least not at reasonable cost. (Actually it is much worse than that, but let's save that for another time).
The barriers of entry tend to be higher when so many parameters have to be figured out and adapted to in a software project. Go appears to have fewer such barriers.
I haven't done any large projects (200kLOC+) in Go yet, but I don't quite see how C++ would make large projects much easier. C++ itself is hard. It takes years to learn. Add to that the complexity in having to decide what subset of it to use and what C++ culture to adopt, and you might have to compromise on comfort from day one. Skip this discussion, and there's trouble further down the road.