Any Console output?
I don't have any console output right now, but I can report that I switched from Unity/Compiz to Cinnamon/Muffin, and now it completes the connection and is playable (albeit with poor performance). An earlier thread mentioned window manager blocking IO, this seems in line with that idea.
Check proprietary video-drivers and if OpenGL is functional (maybe 'glxgears' give a idea of the render performance by now). When i switched from Ubuntu 13.04 to Linux Mint 15 last week games were too slow, dropping performance, graphical issues and Console output telling me that no OpenGL render was found. It was the video driver. Even installing the recommended one from "Driver Manager", had to download the most recent and install it to get OGL to work.
Yeah, switching to the proprietary drivers did the trick for performance. I wasn't going to mess with it until the connection issue got sorted out. Unity seems to be the issue there.
Closing as Ubuntu 13.04 is no longer supported upstream and this appears to have been an issue with Unity DE.
Nothing extracted yet.
Just switched to Ubuntu, clean install and other Steam apps work fine so far. When I try to connect to a server it starts loading and stalls out at ~75%, as reported in at least one other issue thread.