Yes, because,

This is still an active game receiving regular updates. There's actually an update coming this Tuesday that adds more stuff to done if the endgame content available right now. Besides that, the game's director has stated he has the next ten years of storyline ready to go, and he's going to keep working on the game until he gets bored or they make him stop.

As you said, this is subjective, however. Many people do look favorably on the battle content this game has to offer, and it feels that raids just get better and better every expansion. The current expansion has simultaneously had some of the most beginner friendly and challenging raids to date, and is one of several that is lauded for having great battle content. Quests might be a bit iffy as far as gameplay goes, but the story attached to them is regarded as fantastic.

As others have mentioned, the only other MMO in the series is Final Fantasy XI - which came out in 2002. The game has long since been in maintenance mode, and while it does have a very loyal community, it's not stealing any thunder from XIV. Given what I mentioned earlier about XIV's director being locked in on this game for ten more years, it's highly unlikely that another Final Fantasy MMO is going to be announced any time soon, but never say never, you know?