when I started playing arma it was a great game for me at start with so much realism other games could not provide. I used to play on arma server where there was around 80 people playing 40 vs 40. We all had ranks and stuff, conquering positions and on another weekend we would continue where we stopped last weekend. There were guys that flew only choppers and getting other infantry to their positions, recon and so. For me it was a blast cause mixing realism and multiplayer on a big scale was like fighting in a real world but on virtual machines.
Also think they rushed arma2 to get out to the stores cause of OF2 coming this autumn and OP2 has more publicity cause of its commercial agenda.
I look it this way: if OF2 be a better game at least I will be trained to play it by gaining experience in arma2 as both will be very close in its behavior.