you're crazy. the only game better than OFP was R6 Rogue Spear. even Ghost Recon wasn't as good. I mean, Bad Company plays exactly like OFP, only the AI is stupid, and the maps are linear.
I never played ArmA, but ArmA2 has a weak single player campaign, so I could understand how somebody would have dropped it. still, the stuff you can do with the engine, some of the user-made cooperative missions are very intense, and BF or CoD could never even get close to that. the AI is smart. they flank you, they use everything they have at their disposal, they use suppressing fire. on top of that one bullet can easily kill you, so you have to be cautious. you can't just take cover and regenerate health.
for example, there is this mission where you need to take over a town. there are enemy troops in there, some vehicles, there's also a radio tower, unless you destroy it with satchel charges, the enemy will be receiving constant reinforcements. if you get shot your pals will have 5 minutes to patch you up, or else you'll bleed to death. so you have to stick close to your group, scout out enemy vehicles and stationary defenses, call in an air strike or get a bunch of AT guys and provide fire support, get close to the tower, destroy it, eliminate the opposition and finally sack the town. you cannot do this alone, under no circumstances.
compare that to the "kill a wave of enemies, proceed to the next checkpoint, watch a cutscene, rinse and repeat" routine.
ArmA2 is easily the best military shooter out there, most people just don't have the patience to get used to the controls and UI.