Impression from my experience of driving one class from 1-50 and doing some of the endgame.
Quests and Combat
There's nothing to sugar coat it, questing is bad. It's almost bad enough to put you off the game entirely. Without FATEs (public events), class quests and the better parts of main story to fall back on I wouldn't have played long enough to reach max level. The prime example is a quest chain leading in to a fight with the Primal Titan. This section falls into MMO stereotypes so strongly it starts to resemble the introduction to Banjo Kazooie Nuts & Bolts, a section that parodies Rare's increasingly excessive use of collectibles. Without a hint of parody ARR sends the player on half a dozen meaningless fedex quests to prepare a banquet before the NPCs judge the player to be worthy of fighting Titan. The rest of the quests fare little better, constantly sending the player around the map to talk to NPCs despite even providing a lore reason for an ability to communicate at long distances. Side quests largely consists of moving to a location, fighting three monsters that spawn and returning to the quest giver. FATEs are better but struggle to match Guild Wars 2 and mostly consist of tank and spank bosses, AOE spamming regular mobs or collections.
Surprisingly for an MMO it's difficult to play with friends outside the endgame. Quests cannot be shared or replayed and story quests make heavy use of solo instances that require a player to leave a party to enter. The Chocobo companion also suffers from these limits as it is incompatible with instanced events and can't even be used at the same time as a duty finder queue. I saw a lot of players excited about the prospect of unlocking the companion at 30 and then rapidly gave up using it due to these limitations and it's glacial leveling speed.
When it comes to combat ARR comes off better but still doesn't shape up. GW2 set a new standard when it came to class abilities with interesting abilities that were fun to use. ARR's abilities are too flat, not a disaster but unsatisfying and unimaginative in comparison. The multiclass systems is a welcome change from other MMOs, changing class is as simple as equipping the right weapon. Like The Secret World you can spec in multiple classes on the same character, although you must be playing as that class to get XP for it. The system is well designed, letting you save gear load outs and giving you a special inventory with 25 spaces for each equipment slot as well as your regular 100 slot inventory. However the lack of replayable quests comes back to haunt you and even just your second class will require a lot of grinding FATEs for XP.
Dungeons are competent but have a lack of imagination outside the bosses. I didn't feel that they compared well to WoW as they take too long and outside of a few dungeons they pad the duration with trash without any interesting mechanics or providing a meaningful skill check. Cutscenes are a nice touch but prove a hassle when you have done a dungeon several times. Limit breaks make for an interesting change. Charged up through combat they can be saved for difficult spots, twice I've seen healers bring back a wipe by resurrecting most of the group with a level 3 LB.
I can't talk about dungeons without mentioning the issues with the dungeon finder. Without a group it's glacially slow for a DPS with queues of 30 minutes off peak, matching or taking longer than the instance itself. There's also an issue where at peak times a limited number of instance servers causes delays even with a group taking the DPS queue to a jaw dropping hour.
Graphically ARR can produce some great screenshots but overall it's not on the level with GW2. There's an flatness to the look from an ever present lack of contrast. Characters have a very high minimum brightness which can make them look superimposed on the screen, the blackest shadow at midnight is barely any darker than standing in the bright glow of the moon. Characters and gear also suffer from a lack of skin detail and gear with low polycount, small textures and basic shaders. I'm not expecting every MMO to be TERA but I'd at least want them on par with Rift from two years ago, as it is ARR characters are only a notch above Everquest 2. It's testament to the ability of the art team that it's not actively noticeable. They have clearly worked for things to stand up to a pulled back camera.
There's an unfortunate lack of armor designs with multiple pieces recycled at different levels. You'll see lower level sets reused with some texture variations, depressingly the second token set is just your job armor with some minor changes. Feel hundreds of hours of dungeons pay off with a set that could be easily confused with the gear of a fresh 50!
The endgame features four level 50 dungeons, three primal boss fights and the hardcore endgame instance Binding Coil of Bahamut. Every job will be given a set of blue quality, item level 50 job armor at level 45 to ease them into the end game. This is adequate for all the level 50 dungeons and the first primal. You also get a quest for a best in slot weapon although acquiring it is far from simple, the majority of your grinding will be without it.
There's a lack of suitable dungeons at 50 which causes a problem with grinding. Two of the dungeons, Castrum Meridianum and The Praetorium, are used for the story plot and drop no gear, none of the second tier of tokens as well as featuring a large amount of trash, cutscenes and minibosses that slow them down to 30+ minute slogs. Wanders Palace drops a poor amount of tokens for it's clear time and again none of the second token tier. The dungeon Adampor Keep drops ilevel 60 gear and the higher tier of gear tokens as well as being possible to clear in 15 minutes so prepare to grind it constantly. The three primals are single boss arena fights that drop a single weapon and a tiny amount of tokens, no reason to rerun them once you get their weapon. With a 1/9 chance of getting your job's weapon and then probably having to roll for it the grind is again stacked against you.
I have not yet been to the Binding Coil of Bahamut as it's tuned for full ilevel 70. I'm not rocketing towards this quality of gear. It takes five Adampor Keep clears for the cheaper of the first tier of token gear and much, much more for the second tier with a miserly weekly cap that can be filled in just eight clears of Adampor Keep. It might be for the best that players can't clear the end game in a few weeks but a single viable dungeon was unnecessary.
There are some concerns about the economy. A trickle of gil comes to high level players through dungeon rewards but is no competition for repair costs. Similarly FATEs give an insignificant amount of gil, once a player has done all their quests they have no significant source of income outside of trading. With fresh money mainly coming from new characters it's not clear if endgame players will be able to reliably cover their 5k repair bills.