It's best to think of the game as a single-player RPG at its core, though with a lot of multiplayer aspects around it. It's still a Final Fantasy game, or more like a series of them now. The story is long and you have the main game and a lengthy post-credits phase for each expansion.

The first game (ARR) is unfortunately a bit slow, but the expansions build on the characters and events of it so it's not good to skip it.