Singleplayer is very boring, due to the lack of maps that come with the game. Also, there's only one game mode in single player, so that's gets boring very quickly.
Online on the other hand though, is very addictive. There are more game modes, and a few more maps. However, gameplay doesn't change much, but because of their ingenious points system, it gives you something to work towards, and therefore it becomes very addictive.
The weapons customization option is fantastic, and some of the guns are very cool, and is not seen in any other game.