Well, it's an MMO, but I wouldn't put it near that bunch. It has some elements from Guild Wars 2 such as FATES which are events you take part of to gain loads of exp.
The biggest difference is the holy trinity though. You have tank, healer, dps and people in WoW-like games roll a dps to press a certain chain of skills and mostly fap with the other hand, while in XIV dps have more or less the most important role, I'd even say more difficult to play than tank or healer in end-game. There's a lot of tactics for every boss and if you don't know what exactly you're doing you're more or less screwed, but that did exist in WoW back in the day and I've heard WS is similar. Tactics are everything in the game, even more important than gear. You can't really be OP as fuck and solo shit, like, ever. Every single person in the party has a very specific role and if they fail to do it the whole party wipes, including (and especially) if you're dps.
Tanking is very different than WoW too. To begin with tanks barely do any dmg compared to other classes and keeping aggro can be quite challenging, especially for people coming from WoW. Threat meter is quite unique in the sense that you have to constantly be aware of how much threat everyone is generating, because losing aggro is VERY easy. I've seen tanking go very wrong, because of what people are used to in other mmos. Healers and dps have to be very aware of the threat meter too. You can't really go all out and overheal.
I would generally say it's a lot more challenging than WoW, maybe close to what it used to be, but then again, once you get used to it and get the hang of the mechanics it can be easy and fun.
P.S.: inb4 flame wars and 'WoW first mmo' I'm not saying WoW is a bad game. I spent years of my life on it and I respect it as a game and am looking forward to the new expansion. All I'm saying is that XIV is very different.