Way more fun and tense than most games, way more replay value, and the maps are larger than pretty much anything apart from flight simulators (like 250 kmē size).
In addition the mod support is excellent, for example, the DayZ zombie mod was so different and successful it is now being developed into its own game.
While not perfect, everything is superior in realism to games such as Battlefield... for example it is easy to make tank kills at 2400 meters with thermal vision and fire control systems, while in Battlefield 1000m is considered "far" due to balance issues required by the tiny maps.
Not sure why I haven't seen any of you playing it.