My big three.
1, combat. It's actually really boring, there is little variation in what I do, there is never any actual choices to be made in combat in regards to what I should cast. While I expect this early on in an MMO, the very fact that the developers have talked about altering classes to clarify casting rotations (indicating that they want rotations to exist), and they have talked about spam attacks (which should not exist either), says to me that it is this way by design, and will stay this way.
2, linear content design. From solo questing to level 50, up to raiding GSB > RoS > HK. The inability to be able to stop working on one encounter for a week, and instead start working on another that you still have a chance on is really quite limiting.
3, group content. Having to run the same instances at level 50 that were run to get to level 50 - and soon having to do them all again - sucks. It's just repetitive. The lack of a non-instanced dungeon or two is also disappointing.