The AH is a MAJOR issue. Player-player exchanges are really important to facilitate in MMOs. FFXI had one of the better ones. Although, still distant second to the EVE market. But they had one, and it was pretty good. How the hell can they at all justify shipping without one now?
There could be great content waiting for you, but if you can't find the gear to help you get ready for it then what good is it? If you have to offload your junk to the NPC vendors at their depressed prices so you have to farm 3x the drops to afford the gear you need, what good is that great content just waiting out of reach? None.
At the very least there should be no retainers you interact with individually to buy. Just show up at the bazaar and interact with an object (or.. just have some in-town menu, preferably) that opens a window with all items available for sale. Filterable by categories, searchable. If you're selling, drop your stuff off with your retainer, and it shows up in that available list. It should also allow for putting out a purchase order, instead of just the sell orders.
And lastly.. bad UI is bad UI. It may not be literally unusable, but it can be ridiculously more painful than it needs to be which is almost the same thing. It is hardly like Square has no idea what good UI is. They have games with really sensible UI. But what they don't have is consistently good UI, and I can't figure that out. Its almost like they strive to discard the bits that work every time they develop a game.
Either of those issues (AH, needlessly terrible UI design) would be enough to kill my interest. I don't care how great the content may be.. without a worthwhile player economy, its just even more grind to get to that great content. Without a reasonable UI, it isn't fun to get to that great content.