It's a long list, it wasn't just one specific thing that made me quit.

Battle System
Market Wards
Over-sized repetitive Zones, there is no variety
Guildleves get boring as hell after awhile
Too much emphasis on crafting
No class diversity
No content
Low amount of story missions
Lack of story related quests similar to FFXI
Poor animations
NPCs are (a little less now) utterly useless
Party search function isn't as good as it could be
I don't like stat building myself, but I could live with this.