I bought Red Orchestra 2 (RO2) after reader favourable reviews on various websites and it didn't disappoint. There is a decent one player campaign and initial training level but like all these games it's the online play that's crucial. Firstly, the game looks great, and the attention to detail is superb, great graphics, huge maps and plenty of realism. But for me RO2's real strength is in the game play, it's verging on a combat simulation compared to other games of the genre. There's no handy crosshair to target opponents, and when you right click to use the iron sight there's no dramatic zoom in. Spend anytime out in the open, or near a window, and you're dead, don't use cover and run about trying to shoot everyone, and you're dead. This game requires much more patience and skill than most, and the learning curve is thus quite steep. But its the challenging gameplay that keeps me coming back. I was used to playing a game for a week and being on the top of the leaderboards every round, but initially in Red Orchestra I was hardly even getting a kill.
There are various classes of troops like assault, rifleman and even tank crew and you can progress through the ranks by getting kills and team points etc. There is also the usual types of game options such as territory (capture the flag type game), campaign and team death match modes et al so there's something for everyone. There is also a thriving online community with up to 64 players on the maps, and in RO2 co ordinated team play and tactics are especially important. Having a good commander and squad leaders is important and its not enough just to run around shooting away at everything that moves.
If you're a more mature and experienced gamer then I'd recommend this, its a hard game at times, but always enjoyable, and it makes the kills and victories all the sweeter when you get them.