Regarding online gameplay
I have spent the last hour or two, at work, looking up this game. It really looks like my kind of game. I loved BF1942 and the BattleFront MMO. Is the PvP anything like any of the above or the many youtube vids about this game?
I might still get this game if it's mainly about Coops VS computers but that would be a downer.
To be honest, the pvp aspect leaves much to hope for. The missions enabling a hell of an experience are there, but the servers and players aren't.
tried CTI/warfare yet?
See PvP game modes and mission concepts [PvPscene]
To try the game, get ArmA 2 free and join the ArmA2.ru servers and see if you like it.