@mboettcher: the only place you'll see some players its in the Darkzone (PVP area). The PvE map, you're alone if you wan to play solo. If you don't want to play solo you can use matchmaking or invite your friends. The other place you can see players is in a safe area (kinda safe zone).
So this game require an online connection all the time but you can solo the game if you want without seeing other players in the PvE area wile you're doing missions.
Rooten's comments