It does not put modules in GOPATH, at least not where you'd normally find them. Pre-modules github.com/foo/bar would be in $GOPATH/src/github.com/foo/bar. Now they are in $GOPATH/pkg/mod/... (... being based on the URL with some handling for versions and characters that don't work well in filesystems, I don't know the exact details).
The main problems I've had with go modules are fast-and-loose upstreams that happily rewrite history. go mod detects this and stops the world, and you have to manually edit go.sum.
I also feel like "go get github.com/foo/bar" doesn't always get me the latest version. You see that there was a commit 1 hour ago, but then "go get" adds a version like 20181130-93874837 to your dependencies. I assume they know what they're doing? But I'm probably wrong.
The main problems I've had with go modules are fast-and-loose upstreams that happily rewrite history. go mod detects this and stops the world, and you have to manually edit go.sum.
I also feel like "go get github.com/foo/bar" doesn't always get me the latest version. You see that there was a commit 1 hour ago, but then "go get" adds a version like 20181130-93874837 to your dependencies. I assume they know what they're doing? But I'm probably wrong.