Long time WoW player, also played ESO and SWTOR for an extensive amount of time. I started FFXIV recently and it's already my top rated MMO in many aspects and made me seriously wonder why I never gave it a chance before. I'm yet to go through Heavensward and I must say, without even getting to Shadowbringers, this game deserves to be held up with the other big MMOs, and has some great potential.
At first, it does feels a bit odd regarding to GCD, gameplay, and world design, as some aspects of the game were largely limited by the fact the game had to be on PS3. But it's not too long until you get used to it and the story starts getting to you. Once your Job reaches level 30, you'll start having the start of a solid rotation for some classes and the gameplay starts feeling better, and it will continue to improve gradually until your job is fully fleshed out - by then your Jobs should have unique class mechanics that really set the pace on how you play and the 2.5GCD is either straight up reduced or you have so many Off-GCD skills you never really feel bothered by it.
Now this is off course not without its limitations. The game is still a Final Fantasy game, which means it has a very detailed and developed story to go with it, in which sometimes suffers from "MMO filler moments" that includes obnoxious fetch quests and endless mailman mode. There's also a huge quest wall to close A Realm Reborn and start Heavensward, which are unskippable. I hear it does gets better on Heavensward...onwards? (Unless you pay, which I wouldn't recommend as the story is one of the biggest selling points. That said, ARR story is not the best in the game, and could be caught up with some youtube videos.)
ARR as a base game is impressive, especially when you compare to Cataclysm (as they released around the same time). The game clearly lacks the polished look WoW has, especially regarding to its website and account management, but gameplay-wise, it is in some ways better than Cataclysm. What impressed me the most, and I'd recommend any people who may be interested to give it a go is the crafting system. Crafting in this game works as a combat job, as in you have your skills, stats and gear, and the act of crafting an item is a hands-on activity where you can fail, craft a normal or even a high-quality item. (Which I've also heard can be as strong as raid items, so crafting is a valid form of gearing up and the game economy is extremely active because of it)
To finish, I'd have to add that even though the Main Story Quest (MSQ, in-game) is mandatory and sometimes a drag, it does makes the world, especially Vanilla, feel alive by giving players a reason to be in the overworld and running dungeons with friends (as opposed to ignoring the story and chain-queueing dungeons as the best form of leveling). On the good side, the Job system makes it that you never need to level an alt, or re-do the story ever again unless you want it. You can just have the same character learn every job and even get an XP boost for your secondary jobs until they reach your main's level.
Any question you may have about the game itself, feel free to ask me! I'm actually working towards to becoming a Mentor in the future, so I'd be happy to help!