The three official repositories: OSS, Non-OSS, and Update are great and if you ONLY have those 3 then you are doing well and your openSUSE should have minimal problems.
Packman is particularly useful if you wish to have lots of multimedia applications. They also package some games (for example a superb chess game collection). You can surf the site here to see what they have: PackMan :: Startseite
I’ve made no secret over the years that if there was no Packman site for openSUSE, I would have likely stayed with Red Hat/Fedora or moved to Mandrake (before it became Mandriva) and I would NOT have stayed with SuSE / openSUSE . … The importance of Packman to users like me is possibly a bit less today than it was a few years ago, given the massive repository proliferation with the build service, but Packman is still the #1 openSUSE 3rd party repository in my view.
I’ve contributed financially a few times to some of the repository servers.