What we mean: All of us on the team have a lot of fun writing Go. We often show each other little pieces of code that delight us. This seems to happen more when we work in Go than in the other languages we use (or have used), and so we attribute the fun-ness to Go. Pretty straightforward. I'm sorry you're so tired of it.
Wow, I didn't expect to get a response from an actual Googler, working on Go no less. Anyhow, I also remember when people were saying that Java was a fun language to work with, but I still have to find a single engineer who doesn't think of it as slightly more than a pain in the ass. It's all a matter of right-sizing expectations; using and objective language keeps you from being called out should those expectations fail to be matched.
That said, I've already professed my love for the Go language, which I consider the spiritual successor of the C programming language.
Java was fun to play with back in the early days. It was fast, had a VM, garbage collection and was OO. Sadly the fun was gradually removed over the years as a result of design-by-committee and a desire to try to solve some of its core issues.
Fortunately you can still have fun on the JVM, even though I prefer to avoid it these days given its current custodians.
