Battlefield 3 is pretty realistic. Actually, if I'm honest it's only realistic when you're in a vehicle or if you have a tact light/laser in your eyes or when you're trying to kill someone that's more than 100 metres away. The rest of the time it's just a test of your reactions. It's still awesome though.
Unlike Operation Flashpoint, that was like real life (a real drag). You had to travel massives distances to your objectives and you could be killed in one shot if you weren't careful. WHERE'S THE FUN IN THAT?!