Two things:
  1. No Crash on screen switch
  2. Support for playing on dual monitors

Basically, if you have dual monitors, you're screwed right now. The mouse isn't constrained in fullscreen, so you can accidentaly click off screen and crash the game.

It would be nice to have the other monitor serve as an "information hub" so rather than all the on-screen items like chat, hp/mp/tp, exp, map, and everything cluttering the game screen, allow these to be moved onto a second, dedicated, screen.