When it comes to the game's UI, I like that it is customizable and certain things, like the EXP and HP/MP bars can be resized. However, one thing I really wish I could do is change some parts of the UI, such as the mini-menu and Action/Macro bar into a Vertical version and place them on the left-side screen, letting my chat boxes be at the bottom and not obscured.
Seriously. Do this for me, and I'll bake you guys a kickass cake.