Like, as a user downloading packages, or a person packaging an application?
As a user downloading a package, it's been super easy for me and it's been years of running Guix with little to no issue (yet the benefits of rolling release, rollbacks, installing multiple versions of a given software etc.).
As for using it to package an application, I found the challenges mainly in the documentation. This was years ago and a lot of work has gone into improving the docs.
I'm curious what your experience has been.