Criticism 1 - The Ever Shrinking Quest for Quests
Final Fantasy 14: A Realm Reborn is a game constructed around the Blizzard perfected concept of the Quest Hub. This isn't a comparison to WoW insomuch as it is an acknowledgement that Mists of Pandaria's quest hubs were nearly "perfect" by design. The concept of a quest hub is mostly linear and simple.
Here's how it works: a player starts at Point A and does a bunch of quests in a zone. By doing quests, players gain materials to sell, earn new higher level gear, and experience points towards leveling up. Finally, once all the zones in an area are done, players receive a breadcrumb, or a quest that sends them to a new hub. So off they go and the cycle repeats.
These hubs often lead players from one zone to another until that character reaches the highest level possible in the game. So defined, one obvious criticism of quest hubs in general is that they are not dynamic. What I mean is that the quest hub doesn't adapt to a player's level (one minor exception is in Guild Wars 2, where players can lower their level to a quest hub's level), they simply offer static experience based on the pre-defined average experience a quest should offer at that level.
In games like World of Warcraft, the dynamic nature of hubs really doesn't matter because once you reach maximum level, you don't need to worry about any of those quests unless you want to get achievements (gotta get dem'cheeves). However, in FF14: ARR, you do not have a different character for each job. You have one character who needs lots and lots of quests and lots and lots of experience points. Here is where the criticism comes in.
On my first time out on a fresh character on their first job (and maybe on my second), there are a ton of quests and quest hubs to go through. Each of these quests offer a ton of experience and I can level those jobs easily. However, each job I level after the first one takes quests away from the next job I want to level. Eventually, all I can hope to do is grind experience on FATES, Leves (which are finite due to a daily reward of four tokens), and Dungeons.
What eventually happens, or what seems to be happening, is that leveling each job becomes less and less about quests (because all you have are job quests at a certain point) and more and more about the grind. In the beta, without the "wandering minstrels" who granted 15 levels instantly to specific level one jobs, I have no idea what I would have done to get my third or fourth job past those introductory 15 levels.
What this means is that as characters gain levels in the introductory content and as they bring their initial jobs through the game, it will become ever more difficult and time-intensive to get more jobs up to a point where complete customization could occur. Unlocking the advanced jobs, then, will become more restrictive, and reserved for those who have the time and effort to open them up.
Without the full release and a few years, there is no way to know what the true impact of this criticism would be.
Next, another concept from MMOs of old that is quickly becoming an issue: community.