I expect a ton of bad tanks upon release. Mostly from people who don't like/want/know how to tank, but want to lvl a DRK because they just want to take "le epic screenshotz" with their new Au Ra (or their old miqo'te) holding their shiny new greatsword. I expect the other two classes/roles will have similar problems, but not to the degree of the DRK.

Aside from that, I expect just normal launch problems that are usually the result of too many people.