The capitalisation is maybe the most annoying for me, I think it was designed with an IDE in mind (which would be able to automatic update all references), but I still find it a flawed design to have to touch potentially a lot of files, many places to change something from private to not private.
The problem with err has also bit me a few times. I don't like exceptions very much, but a solution like he suggests where a variable can only be ignore explicitly would solve it.
Go is not perfect, but for me there is nothing else better for microservices that I have come across.