-the combat system with its stamina gauge and no auto attacks was horrid
-the game punished mages making no way to get MP other than expensive ethers or a trip back to an aetheryte every 2 fights making it so no one wanted to player THM or CNJ
-lacked a lot of iconic FF stuff (couldn't ride chocobos, no recognizable jobs/skills)
-a confusing class system that left some classes (namely THM and CNJ) for the better part of the leveling experience unsure as to the role as both classes had damaging and healing spells)
-extremely poor translation effort that left even the Japanese players wondering what was going on(look up horsebird fiasco which is what in beta the Japanese maps were plastered with this in the chocobo stable areas where you could inconveniently not pick up a chocobo)*
-lack of auction house
nope

- combat system seemed horrible because of the bad programming
- don't need iconic FF stuff everywhere. Protip : there are FF without jobs.
- one word hasnt been understood and it's automatically a "poor translation"? yeah, right. Besides : http://ffxiv.zam.com/story.html?story=23333
- lol

-server systems made massive lag if more than 1 party was around
-only the best pc's could play the game on anything higher than minimum to medium settings
-fatigue system
-EXTREMELY confusing UI
-a very confusing retainer system used for selling items
Only this. And it's already a lot. The programming in particular, being the very foundations of the game, has effect on everything else.