This is definitely the greatest single player 3d 1st person shooter I've played. It has great AI, great graphics, lots of variety. I'm totally gutted about the multiplayer situation (not being able to join games in progress etc) and the fact that the developers won't be able to do much about the way it is now.
I don't think this game will die as quickly as people are suggesting as long as there are modders and people creating custom campaigns/missions/models etc. This game could definitely been a halflife/quake beater and I bet the developers are kicking themselves for not developing multiplayer as a more integral part of the game.
BIS may have missed the boat here as there are lots of multiplayer games in development or being released soon that will probably take over from halflife/quake style mods.
Oh well who knows maybe there will be OFP2 with mp.