As someone who hasn't used Go, it sounds like GOPATH is very similar to an Eclipse IDE Workspace.
The main difference would be that all dependencies are also in this folder, instead of e.g. a maven or ivy folder located somewhere else. And a (suggested?) folder structure, not dissimilar to java's package structure, where you'd put your e.g. github.com/user/repo repository into $GOPATH/src/github.com/user/repo. I'm sure there's clever tooling or commandline wizardry that works really well with a structure like that.