It's great. If you love Arma. If you don't know or love Arma then the first time you play it, you will hate Arma. It strives to be a highly realistic and highly authentic FPS. Your first 20 games will consists if you spending 15 minutes running to your objective and getting shot by someone hundreds of yards away that you can't see or here. I personally love it because it can be very satisfying after setting up a mission correctly. It's really more of a sim than a "shooter". When played with the right people and in a very patient mind set it can be some of the most fun you'll have PC gaming. Watch many videos to get an idea of how everything works before you pay money for it.
Don't forget taking your jeep into a firefight to run everyone over then to flip off into the sunset!
Thanks! I have played Arma before and briefly played the Single Player missions for the Beta of 3 and it was ok but triple screen support was bleh! Cheers!