My biggest problem with GTA Online has been the load times between a mission and free roam. Every time it loads, I have thoughts have the game delete my character or something.
Oh and trying to get into another person's game, 80% of the time I can't do it. It keeps telling me it's failed, it gets pretty f*cking annoying trying to get into a game when someone invites you to it. Especially when you or your friend are trying to do those 2 man missions.
I'm also unable to join my friends' games. What's your NAT Type? (Network Settings --> Internet Connection Test) Mine is 3 which is what I believe to be the problem.