Arma 2 is a rare success story. Perhaps not merit the game itself but because of the mod DayZ. However that does not take away the merit of Bohemia who created a fantastic game in the genre. Unlike CoD and similar games, Weapon is actually a realistic shooter, a true military simulator. Despite still being in Alpha and the Lite version is not as complete as the normal version, it is not compatible with mods and has no multiplayer component, this version still has all the content needed to make good Arma 3.
The realism of Arma is your greatest asset. Here you can not count on a life bar or the super soldier CoD scheme that stay hidden for a few seconds in the healing of a hail of bullets. In Weapon being hit in the arm implies losing accuracy in shooting and being hit in the leg will cause loss of movement, making the character a limp. Usually games are careful to include weight in bullets, however here this aspect plays a very important and well implemented. Not really a game that anyone can pick up and quickly master, and one of the biggest learning curves in a FPS.