Recently reinstalled this game and patched it up to the latest version.
As already said, makes a big difference to playability if you patch, so get it done ASAP m8.
I've not played online, but I'm working my way back through the campaign missions and really enjoying them all.
Then, after that, there are all the community based missions out there to try. Think that's why I love Arma and OFP, they seem to have designed the game with a forethought to the modding community. Some of the mods out there are simply amazing.