It's an MMORPG, and it is one of the few that follows some interesting story archs with missions and cutscenes. You have to pay to play it; but please do not argue this, it's beating a dead horse if you do.

How long does it take to play? Let's just say I have been playing since 2004, and I still have a hell of a lot of stuff to do. However, I have already completed the expansions (except the Wings of the Goddess one, simply because they are yet to release the final missions).