The main reason to buy this game is the online play. The single players pretty good but the true value comes in the hours and hours and hours of fun to be had in the multiplayer.
Imagine call of duty with much larger maps, much larger teams, the option to spawn on your friends, drivable vehicles including helicopters, tanks, quad bikes, boats, jet ski's, Jeep and so on, dedicated servers (so no cheaters, EA hosts all the games), a great leveling system and great classes to chose from which really changes the game up.
This game is so good even a run on sentence like the last one isn't enough to contain the many, many great things about this game. A bargain at twice the price.