For the longest time I couldn't connect to any games in Far Cry 3 PC. I would get to the "Measuring Quality" screen and the game would stick me in my own lobby that nobody could join. I changed a couple things around on my computer and I was finally able to connect to a game today.
I'm running Windows 8 Pro 64bit. I do not have any third part AV or firewall installed. Here's a list of things I did. I'm not sure which one did the trick so be sure to try them all out.
Update the game to version 1.04
Created inbound/outbound rules in Windows firewall to allow the following ports: