Operation Flashpoint: Dragon Rising is a direct sequel to 2001's hit combat simulation game Operation Flashpoint: Cold War Crisis and the expansion pack Operation Flashpoint: Resistance.
For what it's worth, OF:DR is a fun game to play. It's like Arma, but less focused on being super-serious, on more focused on providing a realistic environment with a story. The missions are adequately challenging, and when you bring along 2 or 3 friends, you can have a good amount of fun.
The game, like any other game, is not without bugs. The AI will sometimes behave strangely, but when you use the AI command wheel, you can tell them to assault buildings, engage specific targets, or even repair vehicles.
The day-night cycle provides a sense of time passage. In the first mission, you start at dusk, and before you're done, it may be night time. The game provides you with night vision, and in some missions you will start in the dark and end in the morning when the sun comes up.
The online servers were shut down, but if you and your friends hook up in a Hamachi network (which is free), you can use LAN to connect to each other for multiplayer. Just enter the Hamachi IP of the person hosting the match, and you're set.
The game is a great deal of fun if you want to play a tactical shooter, but without the bugginess or energy drain of playing Arma. OF:DR is worth a couple of bucks, so pick it up on the next Steam sale.