My concern is that I think that PvP experience exceeds PvE experience by a game imbalancing amount. To the tune of 40% or so, in fact I also am annoyed that PvP gear is better than PvE gear and it has no stat restricting its use in PvE (for those keeping score, games usually fix this by incorporating a PvP stat into PvP gear to make it less effective in PvE).
Mob mixes in zone ending dungeons, while interesting, include too many different interrupts from too many different classes of critter. Making fights painful.
Trickster Rogues are overpowered and likely to be the first class to get the nerf bat. The class may attack out of stealth and remain in stealth...and are almost invincible in resisting the control of Control Wizards in PvP, and Guardian Fighters have an unbalancing amount of mitigation in PvP situations.
The game and setting are beautiful but serious attempts at game balance are needed or the game will quickly run out of control and while the open beta is a solid success, a considerable amount of exploit fixing is needed (AFK'ers in PvP, as noted by ChemKarate I consider an exploit, double eligibility for boss rewards is an oversight, although best I can tell this one is sporadic rather than pervasive but still needs to be plugged).
The adherence to the new Fourth Edition rules is a plus. All in all, a solid game that just needs to be fine tuned.
~J