Despite a terrible launch and slow start, the game has great complexity that grows on you.
The game perfectly executes many aspects of MMO design, but falls short on others. The world is simply gorgeous, quite vast, and populated with many real-time game events. The classes all have their own unique mechanics and feel distinct from each other. They quests are limited in their requests to grind enemies, which is a refreshing change of pace.
That said, there are some major shortcomings. The game boasts of allowing its players the ability to freely switch between and play all classes. While leveling the iniital class is not a problem because of story quests, normal quests, hunting logs, and the myriad events, subsequent classes will be restricted to only a fraction of that well. There are only enough quests to help level 1 or 2 classes at most currently. The resulting experience when switching classes therefore can feel like a grind, which must be repeated for all classes you wish to level. There is nothing preventing players from leveling up alts and thereby avoiding the problem, but it is a problem harshly felt by players who want to use the feature to concentrate on one character.
For players new to MMOs, the game does a very thorough job of introducing them to party roles in dungeons and to various aspects of the game. For veterans of MMOs, the game is slow to start. All game features are locked by quest-gating, meaning players can only unlock certain features of the game by reaching specific minimum level requirements and then completing a (often solo and instanced) quest. To further exacerbate the issue, players must begin in specific towns depending on their classes, which means if you want to play with friends, you must spend an hour walking to the other player's town or play until you unlock instant travel between towns. These two features actually discourage players looking to group up with friends or significant others from the beginning of the game.
This feature seems designed to slowly introduce new players to the mechanics of their classes so they do not embarrass themselves during group play at level 15. For many veterans however, this tutorial system will seem unnecessarily extended. Dungeons begin as initially easy affairs with little or no complexity. Each dungeon introduces specific mechanics that players are recommended to master before continuing to the next dungeon. This is great for new players, but veterans may not feel sufficiently challenged or interested in these features. Along the same thought, players familiar with GW2 will not be impressed by FATES, which lack in diversity and impact to the world compared to GW2's real-time events. Some of those problems can be resolved by future content patches however, so the issue seems moot in light of the other content.
Many mechanics of FFXIV are also closer to games like Everquest, not WoW, which may be jarring to players unfamiliar with the pre-WoW MMOs. This is especially evident for players after experiencing their first dungeon. There is an increased emphasis on teamwork between all members rather than a few key members. After introducing players to the content and explaining how players can use it, the game is content to let players simply choose how to pursue leveling their character. Some like to run quests, others like to grind dungeons, and some will just kill monsters in the open world. The game does not guide you from quest hub to quest hub, resulting in some players running around without an idea of what to do at their level.
There are other features that are missing as well, most notably voice acting, but content such as players-vs-player, housing, and "hard-mode" dungeons has already been prepared. The content is actually finished (as evidenced by pvp and housing trials during open-beta 3 and open-beta 4), but developers are waiting for the majority of players to reach end-game before releasing it. One can only hope that they are also bug-testing it and preparing their servers to avoid a repeat of their relaunch issues. The new team already failed once in that regard, but only time will tell if the development team will be able to meet with the community's expectations.
To wrap it up, despite a turbulent launch and a wildfire of a server problem that rivaled the 1871 Peshtigo fire, the majority of server problems have been resolved. If you're willing to invest a few hours to get past the initial quest-gating, the game proves itself to be quite addicting.