Arma 2 Online is the most intense military simulation i've ever played. You also get really attached to your squad mates in the hardcore servers. Once you're dead you have to wait for the next shipment of people.
please never defile my favorite video game ever again
ARMA 2 (there is no 'ARMA 2 Online') is not just a military simulation, it's a game. The aspects are trying to make it a simulator, but it's also just for fun. Screwing around, practicing, working together, working against each other, etc...
servers all have different game-modes so you can't define the game on a single game mode, nor by the 'once you're dead you have to wait' which isn't true, because different servers have different respawn/revive mechanisms.
pls play the full game and try more than just one mod / vanilla / one server before writing a review of the glorious franchise that is ARMA
on topic: buy arma 2; combined ops... or better yet, the entire arma 2 pack.
You won't regret it.