I have been playing this game since before ARR. The following issues are mine and mine alone, though I am sure there are people who will agree with me.
1. As said in several other places this game isn't friendly to couples are friends. Can you level together? Sure. But lets say you started playing and your friend see it and is like oh man this game looks badass, so he goes out and buys a copy. Really he won't be able to play with you unless you Q dungeons with him. But the way the game currently works this is a bad idea. For those reading, the game currently works like this for new players. New players get a massive exp boost to 70 ( i think ), if a new player starts and spams dungeons so they can play with their friends they will out level the main story quest, along as any quest hubs. Keep in mind these quests hubs also have quests which have to be completed ( though not the main story questline ) in order to be able to fly in some areas, as well as opening the beast master tribes. So really, on your first play through the game is about 100% single player with the exception of a few dungeon ques for trials, dungeons, main scenario quests. Once you get to max level, this is where the game more or less becomes a standard run of the mill mmo. Change to another job and bam without any quest to hold you back, you can play with your friends all the time, almost everything you can do for exp you and level sync down and join in fates, dungeons etc.
2. Lost and forgotten ideas or implementations. The game are riddled with these. It starts in the very beginning but becomes more apparent the longer you play. For example, when you first start the game you play as a main job ( gladiator etc ) once you level up a bit you have the choice to go as a more specialized version of this job ( gladiator to paladin ). The reason for this is they originally wanted you to have cross class abilities. Like in any other MMO isfyou try to be the best you can be you would level up the sub class for the cross abilities, which weren't game breaking but were helpful to squeeze out that little bit extra dps, tankability, or healablitiy. A few expansions later they have all but removed this. All the effort people put into leveling up jobs proved to be 100% useless. Another example are fates. Fates are open world random events ( though they aren't so random ). For the first two real expansions fates were a way to level up, now they are barely noticed unless you are trying to do something specific, yet they are in every zone. The list goes on but I think you get the point.
3. Raiding. For long time in MMOs you have a tank, healers, support, and dps. The tanks job is to work on maintaining control of mobs, while also generating hate making sure mobs aren't hitting other targets. Healers make sure the tank and the dps stay alive, support typically help the dps do more dps, while the dps are ultimately responsible for killing the mobs. This trifecta is standard in most mmos. In final fantasy both raiding and dungeons tanks primary job is to pop a cool down on tankbusters ( hard hitting abilities ), taunt switch, and to do dps ( in that order ), healers jobs are to do dps, raid heal time to time, and heal the tank after a tank bust ( in that order more or less ), dps only job is to not stand in orange stuff, while supports ( if you would even call them that ) is more or less to dps. The game puts such a tight dps check on most raids meaning they can't break this cycle.
4. Diversity. You would think in a game like this where the sheer number of jobs means tons of diversity, but, that isn't the case. Take the tanks, they all have more or less the same # of cool downs, the same abilities etc. Gunblade and Paladin have almost the same 3 hit combo just renamed. Healers all more or less heal the same, at first glance they look different, like oh cool one has cards, one is a direct healer, one has a pet how freaking cool. But at the end of the day all three healers have 2 damage abilities, one of which is spammed until something needs healing ( which isn't as often, most of the time is scripted ).
5. Ability Bloat. Ive played WoW, Rift, EQ1, EQ2, Vanguard, Wildstar, honestly FFXIV has the largest scale of ability bloat in an mmo I have ever seen. Again I am going use paladin as a reference, but you can literally do it with every single job. Paladin has a 2 hit combo, with 2 different finishers and several off gcd abilities which can be weaved thats just for single target. They have a 2 hit combo for aoe, along with another 3 hit combo aoe and a 3 hit combo for single. Without naming abilities pulling trash mobs these are the keys i used. Alt 3, Alt 4, Alt 5, Ctrl 3, Ctrl 4 ( 4 times ), Ctrl 5, then back to Alt 3, Alt 4, Alt 5, Alt 4, Alt 5. Again I am not putting in the abilities which can be weaved, and thats just for aoe, including no cool downs. While reading this you might be like wow this guy must never lose threat, you are right I don't but then again I could just you Alt 4 alt 5 alt 4 alt 5 and I would achieve that goal. But here is the real kicker they don't allow macros at all ( kind of ). If you write a macro for abilities you have to put like 2.5 second pauses between each abilty you use, even if they are not on the GCD. For example lets say you wanted to blow all your cool downs in a single button ( which are instant cast ). You would have to write a macro like this cast ability 1, pause 2.5, cast ability 2, pause 2.5 meanwhile once you create the hotkey, you can't use a single ability during it because it will interrupt the macro.
6. The community and ToS. People say the community is nice and people are great etc. But that is a total misconception. Most dungeons start out with everyone saying Hey then we don't speak the rest of the instance. Come to think thats pretty much in every aspect of the game. Then when you give someone a tip about how to be better they fly off the hinges. Even if you are the most polite person in the game. Me personally if I am doing it wrong I welcome someone to tell me so, the difference is I don't care if they are rude or polite but that is my mentality. Also square enix will suspend or ban your account for cussing, being rude, or just in general being a troll. This alone causes most people just to remain silent.
All in all this game has been remade once. The game is a decent game but misleading in its capabilities.