First thing I can think about is, allow people to change game settings in the launcher itself. Many times I’ve seen people complaining about being unable to do that, because they might be able to play the game on lower settings, but as the game comes with default settings on first launch, they, sometimes, can’t even get to open the client.
Next isn’t as important as other stuff, but would be nice to see. Allow the player to move the launcher around the screen. Now, why is this annoying? Because some people like to use the Windows toolbar on the upper side of the screen (take myself for one xD) and the top part of the launcher sits underneath the toolbar.