Operation Flashpoint. The soviets invade this chain of islands with NATO forces stationed on them. You play as an American Soldier as you fight the commie threat.
If you get the Gold edition, which is around $30 on Amazon.com, you also get two expansion packs. In the first expansion pack you are a Soviet soldier. In the other expansion pack you are a member of the resistance.
In the game you fight as infantry, tank commander, helicopter pilot, jet pilot, and maybe some other stuff in between.
There is a lot of fun to be had with that game. One of my favorite games ever.
It came out at the same time as Ghost Recon. GR got all the fame though and OFP didn't do so well. But many would agree that OFP was the better game. I would.