Going by the name of Arma: Cold War Assault nowadays, Operation Flashpoint is the first installment in the ARMA series (no, the later Codemasters games have less of a relation to this game than the ARMA games!). Its defining feature is combined arms, allowing you to be a foot soldier, tank driver, pilot, and everything in between. Think of it as a GTA for military simulations.
This is probably the best ARMA in terms of a campaign. It is well paced but challenging, and has a coherent plot, at least compared to the latter games in the series. However, since it is a rather old game, the shooting/driving/flying mechanics aren't as well refined as the later games.
Rebels watching for Soviet troops.
Commanding the M60 Tank.
Leading an invasion squad.
A-10 Warthog formation.
"Stay out of the road if you want to grow old." Use the terrain well, and always be aware of the enemy. Engage only if you think it will be beneficial. Do not attract unnecessary attention to yourself.
The game is old, and though you might think you can crank up the settings to max even on a toaster, it is not optimized well. It uses only a single core. Draw distance is best kept at 50-75% of the max settings, as this determines the overall performance of the game.