Another thing worth mentioning is that there are (well, maybe "were", I haven't tried again since a few weeks go) problems getting the game registered. The Rockstar Social Club wasn't letting people login and no one could get the game running. There's some heat on this over on the Steam forums.
Some say this was because they upped priority on the GTA-V Social Club servers or whatever since that was recently released and deserved priority.
Either way, I downloaded it, installed it and could not login/play the game until I had registered (or whatever was needed) because the RSSC was down.