Unbelievably, we actually have Steam for Linux!
The first version is made for Ubuntu, but fear not, it can be installed easily on openSUSE, with 1-click. Just go here and choose your openSUSE version. Click on “Show unstable packages” to see the “1 Click Install” link. Fear not, it’s stable enough to use. In the window that opens you have an check-box that is ticket by default “Remain subscribed to these repositories after installation”. I would not recommend that, because it’s not a good idea to subscribe to a lot of repositories, it can create a mess.
After you installed Steam, you will want to be able to see video previews of games. Because Steam is 32 bit, it will need a 32 bit Flash Player. Most likely your computer is 64 bit and the Flash player is 64 bit too. What you need to do is download the 32 bit .tar.gz from Adobe. Then copy the file libflashplayer.so from inside that archive into /usr/lib/browser-plugins. You have to be root to do that copy operation. Only that library is enough, ignore the rest of the files.