One last point I'd like to make (since some of you here have brought up things you like/dislike about arma/ofp)...
Arma's strong points have nothing to do with its campaign or its included missions out of the box (which all are done poorly IMO). The grandness of Arma is what the community has made out of it themselves with addons, mods and 3rd party missions for free download. There are countless weapon and vehicle addons, sound addons, weapon addons, tons of missions and gametypes, maps etc all for download which make the game what it is and why it keeps going for so many years for some of us.
Arma and OFP are essentially open architecture shell games...somewhat like MS Flight simulator, where you dont expect the greatest content out of the box initially but KNOW and wait for what will be forthcoming from the community which will make it worth more than its weight :-)
As with all games there are many annoying faults with it, but all in all when you take into consideration how there is NO other game title that offers such complete dynamics/changing outcomes with maps large enough to take hours to drive across from one end to the other, it becomes a no brainer to see how that can vastly increase a games replay value, and HAS.
Some of you should try playing some of the missions that were made using the 3rd party DYNAMIC AI (ive made a few mission myself with this)...you can play these sorts of mission over and over and you wont know where the enemy will be comming from or how many you will come across while completing objectives...theres no other game that offers this on such a land scale like this. On the crap side of things the AI is pretty stupid most of the time, the player movement and aim is slow and clunky in feel (both said to be vastly improved in arma2 by the devs themselves) and fps performance can be low with too many AI running around or if you have an older machine.
If you can get passsed its short comings its really hard to find a simulation type game like this which offers such huge value and years of playtime...even if it does still make me curse all the time, lol.