Personally for me only a few things I would not like to deal with again from FFXI would be
1) Useless Crafting Skills... Some crafting was viable to do in FFXI but for the most part it was to costly and to a point non-beneficial. If I'm gonna drop thousand upon thousand(even millions for that matter) into a craft I want it to be for a reason not just to raise a number and never use again.
2) The ability to do missions and levels outside a group. Spending hour upon hours looking for a group to just get the last 15% of a lvl was just obscene and aggrivating. Yes I know some classes could solo and solo decently but outside those 2 or 3 classes there was no chance at it at all. I the more soloist type mmo player for the most part at least when it comes to leveling I dont like having to depend on other(i.e. groups) to get my lvls done give me a option.
3) This ones minor and might not be a big deal to some but an AH that I can list everything i want to sell at one weither it be 2 items or 100 items. 7items at a time sucked and was irritating.
4) Lastly let me have more then one character Please!!!! I know there really wasnt much need for it outside a mule character but I would like to be able to create more then just one char without having to pay for an extra slot to do so.
Now some of these they might have changed in FFXI since I last played Ive been out for almost 3 years now but when I was there those r the top 3 things that irritated me the most.