Yup, was a big Op Flashpoint fan, used to design missions for it and stuff like that. For some reason Arma doesn't quite seem to have the same spark of excitement for me as Flashpoint did, but I think that might simply be because the open-ended approach to completing missions was so innovative for Op Flashpoint, that I kind of take it for granted in Arma. Arma is still streets ahead of most other FPS games and runs great with all the graphics on full throttle too, which makes a change these days!
I do love the fact that you can still do the missions in any way the hell you like, for example the one where you have to destroy the armor in the base at the beginning of the campaign, I tried the stealthy approach loads of times, but couldn't manage it, so in the end I infiltrated an enemy camp, stole a helicopter and strafed the living crap out of the armor in that chopper with an enemy chopper coming after me (which I shot down), funny as hell and mission accomplished.
I certainly do recommend it if you like a game where you can 'do your own thing' with the tactics.
Chock